We present the design of a 100 W high repetition rate photocathode drive laser system for realizing high average current operation of the superconducting accelerator at Peking University. To achieve good beam quality and reliability, we choose photonic crystal fiber (PCF) as the gain medium of the main amplification unit. In addition, we address several key issues for the drive laser system, including the evaluation of the output power of each amplification unit, the design of pulse stretcher and compressor, the optimization of free space coupling setups for pump pulse and seed pulse, etc. We also combine a high-speed semi-conductor optical amplifier (SOA) optical switch with a low-speed acousto-optic modulator (AOM) to achieve the necessary diagnostic mode for the intense electron beam accelerator. This unique design is of importance for the photocathode drive laser with the repetition rate around or above 100 MHz.