Evaluating interventions to improve the mental health among university students in China is a critical priority. Depression, compared to other psychological problems, is one of the most commonly occurring disorders and is associated with school-related impairment and risk of suicide. The aim of the current study is to obtain estimates for design of future definitive trial and obtain preliminary evidence of the effect of a computerized positive mental imagery training intervention, which consisted of 8 sessions delivered across 4 weeks. Participants use ambiguous cues to generate positive scenarios repeatedly from a first-person perspective. In the current study, the BDI-II, PANAS, and RRS were measured at baseline, post-training, and 4-week follow-up. Forty-one participants were non-randomly assigned to either the intervention training group (n = 22) or wait-list (n = 19). Results showed an attrition rate for interventional group was 20%. In addition, group × time interaction for depressive symptoms, positive and negative affect, and rumination, with the intervention group demonstrated better outcomes than controls across time. The largest treatment gains and clinically significant improvements were observed at follow-up. Positive mental imagery training was successfully tested with an acceptable attrition rate. Preliminary results showed that it improved Chinese university students’ depressive symptoms, mood, and maladaptive thinking style. Future larger scale intervention trials are needed to further evaluate the efficacy of this intervention among Chinese university students.