Objectives Through a systematic review, to summarize and describe various health security mechanisms of protecting financial risk from illness in low and middle income countries (LMICs), and to analyze causes that lead to different effects in financial risk protecting. Methods Search words were chosen by both health policy experts and search coordinators after discussion and pilot. Twenty-four electronic databases, websites of 11 health institutions, and the search engine Google were searched. Any original study to evaluate the role of financial protection of health security mechanism in LMICs was included. Pre-designed data extraction form was used for collecting strategies and study method of included studies, and extracted information was analyzed and described. Results Fifty-two studies were included, and 56 specific health security mechanisms were categorized into 6: community-based health insurance, social health insurance, health sector reform, subsidy, user fee, and new rural cooperative medical scheme (NRCMS) in China. Forty-two mechanisms had positive effect in financial protection, 6 were negative, 5 had no effect and the effect of the other 2 was unclear. Conclusion Mechanisms that produced positive effect can be summarized as: setting up of co-payment rate, design of benefit packages, providing free care for vulnerable population, delivering primary health care directly in remote area, and Chinese NRCMS. Mechanisms to protect the poor from financial risk of illness include: government provides health insurance, providing free care and setting up different co-payment rate according to income. The failure of health security mechanisms can be ascribed the deviation from its original goal of health security mechanism design, due to various inner or external causes.