To preliminarily evaluate the clinical efficacy of the renin inhibitor SPH3127 Tablets in patients with mild to moderate ulcerative colitis with placebo as a control and determine the recommended dose.

Inclusion Criteria:

1. Aged 18 - 75 years, male or female;
2. Subjects who have been diagnosed with ulcerative colitis；
3. Subjects who agree to take effective contraceptive measures with their spouses throughout the study period and for up to 12 weeks after the last dose;
4. Subjects who thoroughly learn about the nature, significance, possible benefits, possible inconvenience and potential risks of the trial, understand the study procedures and voluntarily sign the informed consent form prior to their participation in the trial.

Exclusion Criteria:

1. Subjects who are diagnosed with Crohn's disease or indeterminate colitis;
2. Subjects with active infections at screening which may, as evaluated by the investigator, cause increased risks for subjects;
3. Subjects who had surgery that might impact the absorption of oral drugs, subjects who will undergo surgery during the study period, subjects who have undergone major surgery before screening, or subjects who have a plan of surgery during the study period;
4. Subjects and lactating women and those who will become pregnant within 6 months after the trial starts;
5. Subjects with a history of drug abuse with clinical significance within 1 year prior to screening;
6. Subjects with other diseases or conditions that the investigator considers unsuitable for this trial.