Objective To explore the application and influence of the whole course mentor system combined with OSCE on the critical thinking ability of undergraduate clinical student nurses. Methods 176 undergraduate clinical student nurses were divided to control group and experimental group,88 for a group respectively. Control group used traditional clinical teaching method while the experimental group used whole course mentor system combined with OSCE. The theory and practice assessment scores ,medical record writing scores and critical thinking scores of clinical student nurses before and after the implementation of the two teaching modes were compared. Results The theory and practice assessment scores and medical record writing scores of the students in the experimental group were better than those of students in the control group（P<0.05）. The score of CTDI-CV was increased in both two groups after intervention. The score of all dimensions in CTDI-CV was better improved in the experimental group than that of controls （P<0.05）. And the evaluation of teaching mode of the experimental group was better than the control group（P<0.05）. Conclusion The teaching method of the whole course mentor system combined with OSCE is helpful to improve undergraduate clinical student nurses'ability of critical thinking.