Objective To explore the impact of training program based on the Theory of planned behavior (TPB) on nursing undergraduates' knowledge, attitude and practice (KAP) of safe injection.Methods Totally 80 students from the nursing students in internship from a medical university were selected in 2018, and the students were randomly assigned as the experimental group (n=41) and the control group (n=39). The experimental group was administered a TPB-based safe injection behavior training program on the basis of conventional safe injection education;the control group received conventional safe injection education, including the pre-job training and guidance from the clinical teachers. The scores of knowledge, attitude and practice of safe injection from both groups were compared through KAP questionnaire of safe injection in nursing students before and after the training (1 month and 3 months). Two teachers used the observation table of safe injection to score the students' behavior.Results After the training (1 month and 3 months), the self-evaluation total score and the observation score of aseptic operation andpreventing sharp instrument injuryin the experimental groupwere all higher than those in the control group. In 1 month after the training, the self-evaluation total score of the experimental group and the control group were [(208.34±17.43) vs. (194.18±11.83), P<0.01], the observation total scores of the experimental group and the control group were [(15.20±1.21) vs. (12.03±1.66), P<0.01]. In 3 month after the training, the self-evaluation total score of the experimental group and the control group were [ (204.61±13.52) vs. (194.10±8.18), P<0.01], the observation total scores of the experimental group and the control group were [(13.61±1.14) vs. (12.46±1.10), P<0.01].Conclusions TPB-based safe injection training program can improve nursing students' knowledge, attitude and practice.