Objective: To test whether crowding is much more severe under simulated monovision conditions.Methods: This was an experimental study. Twenty subjects participated in this experimental study from March to November 2015 in Wenzhou Medical University. Both eyes viewed clear images under normal conditions. While under the simulated monovision condition, one eye viewed a clear image (OD), and the other eye viewed a blurred image (0.75, 1.50, 2.50, 3.50 D). The eccentricities of the target in this study were 2.5°, 5.0°, and 7.5°. The threshold of the crowding effect was measured by a staircase method. Two-way ANOVA with repeated measures and a t-test with Bonferroni correction were used to test whether crowding was much more severe under the simulated monovision condition. Results: Crowding depended significantly on intraocular blur (F=13.37, P<0.001) and eccentricity (Ecc) (F=296.90, P<0.001). Significant interactions between intraocular blur and Ecc were found (F=4.03, P<0.001). When the eccentricity was 7.5° or 5.0°, intraocular blur significantly affected the critical gap size of crowding (F=8.59, P<0.001; F=3.74, P=0.01). However, intraocular blur did not affect the critical gap size of crowding when the eccentricity was 2.5°(F=1.13, P=0.34). Conclusions: Crowding is much more severe under simulated monovision conditions than normal conditions, and the difference is dependent on intraocular blur and eccentricity.