The effect of the role on the second harmonic generation of the Q-switched broadband optical fiber laser are simulated by using the methods of grating angular spectral dispersion (ASD), prism ASD, and crystal cascade scheme. LBO crystal type I phase is used to match, by numerically solving the three wave coupling equations of Gauss beam, the incident light frequency width, focal position, focal spot size and crystal thickness influence on the conversion efficiency are obtained, and the parameters of crystal is optimized. The calculation results show that the second harmonic generation (SHG) efficiency is only 17% with the laser bandwidth of 5 nm; the use of the grating ASD can achieve frequency doubling efficiency of more than 70% in a large spectral range; the compensation of the prism is smaller, while can improve the efficiency by 50%; three crystal cascade can make the efficiency increased by 130%.