This study aimed to assess whether a WeChat-based self-management intervention would be effective for community middle-aged and elderly adults with hypertension in Guangzhou, China. We conducted a cluster-randomized control trial with a total of 464 participants (intervention, n = 186; control, n = 276) between March 2018 and May 2019. The self-management intervention lasted for 6 months, consisting of health education, health promotion, group chat, and blood pressure (BP) monitoring. All individuals in the baseline and follow-up surveys were assessed for BP and completed a hypertension knowledge questionnaire, self-efficacy scale, self-management scale, and social support scale. A total of 253 participants (intervention, n = 110; control, n = 143) completed the follow-up survey and were included in the analysis. The adjusted mean differences in the changes in systolic blood pressure (SBP) and diastolic blood pressure (DBP) between the intervention and control groups were −6.9 (95% Confidence Interval (CI) −11.2 to −2.6; p = 0.002) and −3.1 (95% CI −5.7 to −0.6; p = 0.016) mmHg, respectively. Individuals who participated in the intervention program had better BP monitoring, improved their hypertension self-management as well as parts of their disease knowledge and self-efficacy. The WeChat-based self-management intervention may be a feasible and efficient program to help Chinese community middle-aged and elderly hypertensive patients lower BP and improve self-management.