In order to study the influence of process conditions on optical properties of organic photodetector with p-type Si substrate,using the Dektak-8 α-step instrument and high-resolution Topometrix Exptorer atomic force microscope(AFM),the organic film thicknesses deposited on the surface under different conditions of substrate temperature and evaporation were measured.By means of topology and lateral force,contact the variation of the surface morphology was studied.The electro-optical properties photodetector of were tested.The results indicate that the polycrystalline thin film formed on the surface shows island form.The size and morphology of the island are affected by preparation process conditions.When the substrate temperature is 50 ℃,PTCDA evaporation temperature is 420 ℃,and evaporation time is 15 s,its evaporation thickness is 135 nm.The measured maximum photocurrent is 92 μA,and the dark current is 7 nA.The optimal substrate temperature and evaporation condition are realized.