A new positive intrinsic-negative (PIN) phototube is introduced. For the different operation characteristics of the PIN phototube at different conditions, through software simulation and analysis, the variance of the phototube operation characteristics is proposed. Experimental modules are presented to test the variance of the operation voltage, current and the characteristics of the phototube under different illumination conditions. The cause of the characteristic variance is analyzed, and the best operation method of the phototube is proposed, which has certain references in application.