Critical illness insurance to reduce the incidence of catastrophic health expenditure was implemented in China in 2012. The aim of this study is to explore the implementation status and medical guarantee effect of critical illness insurance in various cities.We extracted insurance reimbursement data for 2014 from the critical illness insurance information systems of 4 cities. Characteristics of the critical illness insurance system were used to describe the implementation status. The share of medical expenses reimbursed by insurance and the percentage of individuals suffering catastrophic health expenditures were calculated to evaluate the effect of critical illness insurance.The share of medical expenses reimbursed by insurance was 58.93%, 47.29%, 62.05%, and 61.75% in Beijing, Siping, Yichang, and Zhaoqing, respectively; those shares increased by 5.29 percentage points, 7.72 percentage points, 13.30 percentage points, and 22.63 percentage points, respectively, after the introduction of critical illness insurance. The percentage of individuals suffering catastrophic health expenditures was unchanged in Beijing, but decreased by 7.04 percentage points in Siping, 11.22 percentage points in Yichang, and 2.19 percentage points in Zhaoqing.China's critical illness insurance increases the level of medical guarantee to some extent, but its effect on reducing the incidence of catastrophic health expenditure is somewhat limited.