AIM: To investigate the size of functional optical zone (FOZ) after small incision lenticule extraction (SMILE) versus femtosecond laser assisted excimer laser keratomileusis (FS-LASIK) for myopia correction and potential associated factors for FOZ. METHODS: A total of 133 patients who received corneal refractive surgery in our hospital between November 2018 and July 2021 were retrospectively enrolled. There were 63 patients (123 eyes) in SMILE group and 70 patients (139 eyes) in FS-LASIK group. The size of FOZ was measured using Pentacam 3-dementional anterior segment analyzer before and 3mo after surgery, so as to analyze postoperative achieved functional optical zone (AFOZ) and its contributing parameters. RESULTS: When planned functional optical zone (PFOZ) was 6.5 mm for both groups, AFOZ was 1.45±0.27 and 1.67±0.25 mm smaller than preoperative FOZ in SMILE group and FS-LASIK group 3mo after surgery. AFOZ in SMILE group was significantly larger than that in FS-LASIK group (P<0.001). Variation of FOZ was negatively correlated with preoperative spherical equivalent (SE) and positively correlated with variation of mean keratometry value (△Km), variation of spherical aberration (△SA), and variation of Q-value (△Q, all P<0.001) in both groups. Multiple variable linear regression equations were △FOZ=1.354-0.1×pre-SE+0.336×△Q+1.462×△SA in SMILE group and △FOZ=1.512+0.137×△Q+0.468×△SA in FS-LASIK group. CONCLUSION: AFOZ is significantly smaller than preoperative FOZ in both SMILE and FS-LASIK groups. With the same PFOZ, larger AFOZ is achieved in SMILE group than in FS-LASIK group.