Theoretical simulation was conducted by a model for calculating amounts of liquid crystal，and experiments were carried out for each factor. The measurements for improving uniformity of cell gap were tested on some products. The experiments results showed that PS， altitude difference on array substrate and altitude difference on color film substrate were critical factors affecting uniformity of cell gap， the three factors that could affect the Cpk value of cell gap were 0.9， 0.5 and 0.8， respectively. The Cpk of cell gap could increase 0.6 by using organic on array substrate， while that couldincrease 0.9 by using XPS. The best way to reduce altitude difference among pixels was using OC， which showed that normal OC and highly flat OC could increase the Cpk of cell gap by 0.2 and 0.5， respectively.