Abstract: Switch rail defect is one of the important safety hazards in turnout system. The flat-plate magnetostrictive sensor was used to excite 30, 70 and 100 kHz horizontal shear waves at the bottom of the rail to monitor the head and bottom defects of the pointed rail in this paper. First, the influence of ambient temperature on wave packet energy of the reflected echo of the characteristic structure in the switch rail was studied. The wave packet energy was observed increases approximately linearly with temperature. The method of energy ratio between characteristic signal and reference signal was proposed to effectively compensate the influence of temperature on monitoring results. Second, the guided wave monitoring experiment was carried out in the process of increasing the volume of the rail head and rail bottom defects. The characteristics of the defects and the reflected wave packet energy at the rear end were "first raised and then suppressed", which enhanced the recognition ability of guided waves to the defects. Taking 30 kHz and 70 kHz guided waves as examples, they could identify the rail bottom defects of 20.0 mm in length, 2.0 mm in width and 7.1 mm in depth, and the rail head defects of 38.6 mm in length, 2.0 mm in width and 10.1 mm in depth, respectively. Results show that the magnetostrictive guided wave technology can realize the effective monitoring of switch rail defects, and has important engineering application prospects.