Nursing trainees experience transition shock from theory to practice, which depletes their psychological resources, leads to self-doubt, and reduces moral sensitivity to patients' ethical situations. The cross-sectional study from June to December 2024 used online questionnaires including the Transient Shock Scale, Self-Compassion Scale, and Revised Moral Sensitivity Scales. Transient shock was a key predictor of moral sensitivity with a significant negative correlation (r = −0.320, p < 0.01). Self-compassion partially mediated this relationship, accounting for 42.59% of the total effect. Calling moderated the negative effect of transient shock on self-compassion, and as it increased, the mediating effect of self-compassion decreased. The study recommends strengthening self-compassion and calling in trainees to reduce shock, promote the development of moral sensitivity, and form skilled, empathetic nurses.