Objective To explore the epidemic characters of Pathological Internet Usage (PIU) in the newly enrolled post-graduates and further to detect the relationship between PIU and relative social environment, etc., so as to provide more evidence for the etiology of PIU. Methods Questionnaire was conducted in 556 newly enrolled post-graduate students of a medical university. The recovery rate of the valid questionnaires was 94.72%, and the data were analyzed by chi-square test, t-test and logistic regression. Results The rate of internet-utilizing students in recent one year was 95.3%, thereinto, 5.3% of them was with internet addiction disorder. Multivariate logistic regression analysis showed that the major impact factors were gamble, playing games, the heavy study pressure, psychoticism personality characteristic tendency and low self-respect, the OR values (95%CI) were 13.966 (1.662~117.835), 3.440 (1.401~8.450), 1.249 (1.096~1.423), 0.889 (0.821~0.963) and 2.749 (1.167~6.475), respectively (all P