Objective To explore the effect of Gibbs reflective cycle on critical thinking ability and self-directed learning ability of nursing undergraduates in their internship in intensive care unit （ICU）. Methods A convenience sampling method was used with 150 nursing undergraduates who practiced in the ICU of the Affiliated Hospital of Zunyi Medical University from July 2021 to September 2022. The participants were divided into two groups with 75 students in experimental group and 75 students in control group depending on their time of admission. The control group was treated with traditional follower teaching mode，and the experimental group was treated with Gibbs intervention on this basis among four weeks. Participants completed the reflection diary according to Gibbs，reported and shared the reflection results，integrated the reflection conclusions. The scores of critical thinking ability and self-directed learning ability before and after intervention were compared between the two groups. Results After intervention，the score of critical thinking in the experimental group was（300.33±16.71），while that in the control group was（291.49±11.69）. The difference between the two groups was statistically significant（t=3.754，P<0.001）. After intervention，the score of self-directed learning ability in the experimental group was （151.69±21.95），while that in the control group was（136.99±27.56）. The difference between the two groups was statistically significant（t=3.614， P<0.001）. Conclusion Gibbs teaching method can improve the critical thinking ability and self-directed learning ability for nursing undergraduates during their clinical internship in ICU.