To solve the problem of weak signal of shear horizontal guided wave detection across weld, a time reversal detection method based on SH guided wave mode is proposed in this paper. The low frequency SH0 guided wave mode is selected for this detection. A 3D equivalent model for the defect detection of cross weld on a 3mm thick plate was established, and the time reversal detection was simulated numerically and demonstrated by experiment. Firstly, it is verified that time reversal can improve the sensitivity of post-weld defect detection from the perspective of simulation. Then, the PPM EMAT system was designed and built to generate SH0 mode wave for conventional and time-reversal detection experiments. Experiments verify the validity of a time reversal detection method. Experimental and simulation results show that the time reversal method has a strong focusing effect on the low defect echo signal in conventional detection. This method can increase the conventional signal amplitude to 3.22 times, and can be used to detect 1mm longitudinal crack defects effectively. This paper provides a new idea for conducting wave detection of defects across welding seams.