To assess the effect of oral vitamin D3 supplementation in dry eye after femtosecond laser-assisted in situ keratomileusis (FS-LASIK). Liuzhou Worker's Hospital. This prospective study included 90 patients selected between January and December in 2019, who underwent FS-LASIK operation in our hospital and had obvious symptoms indicating dry eyes 1month after operation. The subjects were randomly divided into two groups: The experimental group (n = 45) received vitamin D3 2000IU/D continuously for 12weeks; the control group (n = 45) did not take vitamin D3 orally. Ocular surface disease index (OSDI), Tear breakup time (TBUT) and Schirmer's test I were evaluated premedication and 1,3,6months after treatment. Serum vitamin D3 level and the mean concentration of cytokine IL-6, IL-17, IL-23 in t ears were also measured. One month after treatment, the mean OSDI score of the experimental group (11.67 ± 8.53) was significantly lower than that of the control group (23.82 ± 13.22) (P = 0.007). TBUT (10.71 ± 1.02s) and Schirmer I (9.36 ± 0.40mm) of the experimental group were higher than those of the control group (7.49 ± 1.29s and 7.51 ± 0.44mm). The OSDI (10.25 ± 5.49) was significantly lower than those of the control group(20.22 ± 6.23) and TBUT (10.75 ± 1.09s) and Schirmer I test value (11.34 ± 0.39mm) of the experimental group were significantly higher than those of the control group (8.36 ± 1.23, 8.12 ± 0.50) at 3months after treatment. There were significant differences in OSDI, TBUT (P < 0.05) and Schirmer I test value between the two groups at 6months after treatment. Serum vitamin D3 level was negatively correlated with OSDI score (r = - 0.90; P = 0.00) and positively correlated with Schirmer I test (r = 0.88; P = 0.00), TBUT score (r = 0.89; P = 0.00) and TMH (r = 0.80; P = 0.00). IL-17 level was shown to be significantly correlated with TBUT(r = - 0.25, P = 0.014) and Schirmer I test (r = - 0.21, P = 0.018). IL-6 level was significantly correlated with OSDI (R = 0.18, P = 0.020) and TBUT (R = 0.20, P = 0.019).