A railway track smoothness detector based on laser reference is proposed, which can detect height irregularity, alignment irregularity and curvature. The detector uses laser as reference and uses gradienter and remote focusing system to make laser irradiate the photoelectric target vertically. The data is collected through the data acquisition unit and is transmitted to the data processing unit. The track irregularity parameters are obtained and displayed on the human-computer interface. The experimental results show that the proposed detector has high reliability and high accuracy. The detection distance can reach 200 m and the measurement accuracy is 1 mm.