The main objective of the study will be to assess the efficacy and safety of Allisartan Isoproxil/Amlodipine (240 mg/5 mg) in patients with mild to moderate essential hypertension uncontrolled after 4-week treatment with Amlodipine besylate（5 mg) or Allisartan Isoproxil (240 mg).

Amlodipine belongs to the calcium channel blocker (CCB) class of drugs, which acts as an antihypertensive agent mainly via blocking calcium channels on the vascular smooth muscle cells to dilate blood vessels.

Allisartan Isoproxil belongs to the ARB class of drugs, which can effectively exert antihypertensive effects.

The combination of dihydropyridine CCBs and ARBs exerts synergistic antihypertensive effects.

Inclusion Criteria:

• Patients 18-70 years old with mild to moderate essential hypertension;
• Untreated patients (either newly diagnosed essential hypertension or those patients with a history of hypertension but have not been taking any antihypertensive drugs for at least 2 weeks before the first visit) must have an office msSBP ≥ 150 mmHg and < 180 mmHg and DBP<110 mmHg;
• Patients who had not received regular treatment with Amlodipine Besylate (5 mg/day) (less than 4 weeks of medication intake or a history of missing doses for 5 or more days within the 4 weeks before screening) with the mean sitting blood pressure of 140 mmHg≤ SBP <180 mmHg and DBP<110 mmHg;
• Patients currently receiving other antihypertensive agents (non-study medications for at least 2 weeks prior to screening) with the mean sitting blood pressure of 140 mmHg≤ SBP <180 mmHg and DBP<110 mmHg, and the clinician determined that it was appropriate to switch to Amlodipine Besylate (5 mg/day);
• Patients who have been stably treated with Amlodipine Besylate (5 mg/day) for at least 4 weeks with the mean sitting blood pressure of 140 mmHg≤ SBP <180 mmHg and DBP<110 mmHg. During randomization for the double-blind treatment period, mean sitting blood pressure should be 140 mmHg≤ SBP <180 mmHg and DBP<110 mmHg;
• Participants enrolled in the ambulatory blood pressure monitoring (ABPM) study should have 24-hour mean ambulatory blood pressure ≥130/80 mmHg after 4 weeks of monotherapy treatment;

Exclusion Criteria:

• Patients with secondary hypertension;
• Patients with msSBP ≥180 mmHg and/or msDBP≥110 mmHg, or with hypertensive emergency or hypertensive urgency.
• Patients with history of heart failure (New York Heart Association (NYHA) Functional Classification class III and IV), acute coronary syndrome, percutaneous coronary intervention, or other serious heart diseases (such as cardiogenic shock, moderate or severe heart valvular disorders, atrioventricular block second or third degree, bradycardia (with a heart rate <50 beats per minute), severe arrhythmias) in the past 6 months.
• Patients with history of severe cerebrovascular diseases (such as hypertensive encephalopathy, cerebrovascular injury, stroke, transient ischemic attack) in the past 6 months.
• Patients with aortic aneurysm, aortic dissection, or dissecting aneurysm.
• Patients with renal artery stenosis or severe renal insufficiency (Cr>1.5 times the upper limit of normal).
• Patients with blood potassium >5.5 mmol/L.

Double-blind treatment (Week 4~Week 16):

Open-label period(Week 16~ Week 56):