Abstract: The high-speed modulated semiconductor lasers are the key devices in the system of high-speed fiber communication and phase control radar systems,etc.The parasitic capacitance of the high speed laser is one of those factors which affect the modulation bandwidth.In order to reduce it,the capacitance of the ridge waveguide structure was analyzed and tested,computer simulation was performed.A conclusion is made that capacitance's value is related to not only the eroded depth of the insulation channel but also the area of the metallization,which is important for the realization of the high-speed modulation of the laser.