Abstract. The article describes the search for optimal geometric parameters of the betatron injector. First of all, we determine parameters that influence the injection efficiency. Next, we introduce the coefficient that directly connects the geometric parameters of the injector with capture efficiency. The computer model of the betatron injector is recreated. In the injector region, there are forces that are equal in magnitude and direction to forces in a real betatron. We simulate different parameter combinations. After processing the results, tolerances are obtained for the selected parameters. The results of this work can be used as recommendations for the development of design documentation for new three-electrode injectors for betatrons. The research method can be used to study the efficiency of other injector designs, as well as to search for new design alternate.