To improve the detection efficiency of deep ultraviolet laser for semiconductor detection, it is necessary to develop 257 nm deep ultraviolet picosecond laser with high power and high repetition frequency. In this study, a 257 nm deep ultraviolet laser was experimentally investigated based on photonic fiber amplifier and extra-cavity frequency quadrupling. The seed source uses a fiber laser with a central wavelength of 1030 nm and a pulse width of 50 ps, delivering a power output of 20 mW and a repetition frequency of 19.8 MHz. High power 1030 nm fundamental frequency light was obtained through a two-stage ytterbium-doped double cladding (65 μm/275 μm) photonic crystal fiber rod amplification structure, and 257 nm deep ultraviolet laser was generated using double frequency crystal LBO and quadruple frequency crystal BBO. The seed source uses a two-stage photonic crystal fiber amplifier to get a 1030 nm laser with output power of 86 W. After the laser focusing system and frequency doubling, a second harmonic output power of 47.5 W at 515 nm and a fourth harmonic output power of 5.2 W at 257 nm were obtained.The fourth harmonic conversion efficiency was 6.05%. The experimental results show that this structure can obtain high power 257 nm deep ultraviolet laser output, providing a novel approach to improve the detection efficiency of the lasers for semiconductor detection.