According to the quantum theory of light ,the necessary condition for the photoelectric effect is that the frequency of the incident light is greater than the threshold frequency. When this condition is satisfied ,the flux of the escaped electrons depends on the flux of the incident photon. When the frequency of the incident light is greater than the threshold frequency , and the flux of the incident photon is delinitc, the flux of the escaped electrons is also definite, However, not all of these escaped electrons reach the anode to form a current In this paper , the physical factors affecting the current under a certain escaped electrons flux are analyzed. The results show that the main factors affecting the current are the applied forward voltage and the electron escapeangle ( the angle between the initial veloeity of the escaped electron and the axial direction of the phototube)'Then by using the graphing method , we examined the influences of 0, and  in detail, and the conclusions show that ,for an electron with a certain 6,, it can reach the anode and contribute to the current only when l isgreater than a certain critical value. While for a certain U, only those electrons with 0, less than a certaineritical value can reach the anode and contribute to the current.