Based on the conduction band electron density and the expression of the effective dielectric function, the absorption coefficient at 532nm of KTP crystal is deduced. The evolution law of conduction band electron density, absorption coefficient and second harmonic generation (SHG) conversion efficiency are comparatively studied. The results are as follows. The 532 nm absorption coefficient of KTP crystal is increasing with conduction band electron density, and the SHG conversion efficiency is decreasing with conduction band electron density. When the power density of fundamental frequency laser is a fixed value, conduction band electron density shows accumulation effects a different repetition rates, which caused the 532 nm transmission and the SHG conversion efficiency of KTP crystal to vary exponentially with acting time, and the accumulation effect is increasing obviously with repetition rate, but conduction band electron density and absorption coefficient approach thir steady values.