The paper collects data of 15 541 physicians in www.120ask.com to conduct empirical analysis on the influence of physicians' online gratuitous treatment on patients' choices. The results show that the quantity and quality of physicians' gratuitous treatment pose positive influence on patients' choices, and physicians' reputation as well as the price of service also remarkably modulates the process. Based on the results, it comes up with relevant suggestions serving as references for the physicians and administrators of online health community.