Surface photovoltage measurements was employed for studying the sensitization mechanism of triphenylmethane dyes from the relationships of the adsorption state of dye molecules on zinc oxide powder surfaces. In the case of the acid type dyes of triphenylmethanes, experimental curves agree well with the theoretical results of light intensity dependences of photovoltage V_p and d V_p / dt . It is found that the acid type dye adsorption on zinc oxide unaffects to zinc oxide intrinsic photoresponse. On the other hand, the Na salt type dye adsorption on zinc oxide shows the desensitization for zinc oxide intrinsic photoresponse, because the adsorbed molecules of the ground state attribute to recombination process of the free carriers photo-generated in zinc oxide bulk. It is concluded that the carboxylic or sulfonic radical of dyes will be mainly attracted to adsorption sites. And the mechanism of dye sensitization on zinc oxide surface is proposed that the electrons of excited dyes is mainly transferred to conduction band through the hydroxyl radical.