Three kinds of ink film thickness and optical density conversion model were established through simulating offset print with IGT. According to the MAE and RMSE values, by using Tollenar-Erns model, the best range of ink film thickness of different paper and ink's combination were solved. A three dimensional model of CCD signal acquisition values and ink film thickness was set up by using v4 interpolation algorithm to realize ink on-line testing. The model's accuracy was validated by testing sample's CCD signal acquisition values on the correspondence to the best range of ink film thickness.