This is a multicenter, randomized, double blind, placebo-controlled, parallel design study to evaluate the efficacy and safety of TPN171H in men with erectile dysfunction.

Inclusion Criteria:

• 18 years to 65 years (inclusive)
• Males with ED at least 6 months
• IIEF-5 ≤ 21 at visit 1
• Patients in a stable, heterosexual relationship for at least 3 months and during the study;
• Patients who are willing to stay away from any other medicines or treatments for ED during this study period
• Patients who are willing to have 4 or more attempts of sexual intercourse per 4 weeks, demonstrated compliance with the study protocol, including drug administration, diary completion, and scheduled study visits, during the qualifying trial;
• Patients who are willing to take proper contraceptive during the study and within 3 months after the study completed;
• At the end of the untreated baseline period, the following conditions are met：（1）The subject must make at least four attempts at sexual intercourse during the untreated baseline period. （2）At least 50% of attempts during this period must be unsuccessful,（unsuccess means at least one of the first three questions should be answered "No" in SEP）.（3）5≤IIEF-EF≤25.
• Patients who have voluntarily decided to participate in this study, and signed the informed consent form.

Exclusion Criteria:

• Patients who have a history of hypersensitivity to other PDE5 inhibitors or TPN171H;
• Patients with anatomical malformations of the penis;
• Patients with primary hypoactive sexual desire;
• Patients with ED, which is caused by any other primary sexual disorder
• Patients with ED ,which is caused by spinal injury or have had a radical prostatectomy or other surgery
• Patients who have a penile implant
• Patients who have not responded to PDE5 inhibitors or who have an adverse reaction leading to discontinuation
• CYP3A4 potent inhibitors, potent inducers, and moderate inducers (except topical drugs) should be used within 28 days before the start of treatment or during the trial period.
• Subjects who are taking nitrate or NO donor drugs, anti-androgens, guanylate cyclase agonists, or other drugs or treatments for the treatment of ED and cannot be discontinued
• Patients with the following cardiovascular disease:
• Myocardial infarction or stroke within the last 6 months; Unstable angina or angina occurring during sexual intercourse; New York Heart Association Class 2 or greater heart failure in the last 6 months; Uncontrolled hypotension (<90/60mmHg), uncontrolled hypertension (≥160/95mmHg); Orthostatic hypotension.
• Diabetic patients whose FBS is over 1.5 fold of normal value, or whose HbA1c >9%, or with diabetes complications, such as diabetic nephropathy, peripheral neuropathy;
• Patients with hepatic or renal dysfunction as per the following: AST, ALT>2*ULN, serum creatinine exceeds 20% of the upper limit of normal value;
• Patients with active gastrointestinal ulcers and bleeding disorders;
• Patients who have a history of NAION, or with a known genetically degenerative retinopathy, including retinitis pigmentosa;
• Patients who have a history of sudden decrease or loss of hearing;
• Patients with a history of severe central nervous system injury or peripheral muscular neurological disease in the past 6 months.
• Patient with a history of malignancy;
• Patients with significant neurological abnormalities;
• Patients with alcohol addiction
• Patients with persistent abuse of drugs of dependence;
• Patients who are planning to father a baby or are in a relationship with a pregnant partner.
• Patients who have a childbirth plan during the trial period and within 3 months after the trial.
• Patients who are participating in the past 3 months from any other clinical trial
• For other reasons besides the aforementioned cases, patient whose participation is deemed inappropriate due to clinically significant findings according to the medical decision of the principal investigator or the study personnel.