Abstract: To investigate the effectiveness of the application of the transient Rayleigh wave method to the quality detection of grouting in karst roadbed, two numerical models were built from the characters of typical geology sections in the field. They are respectively for underground strata with or without karst cave, and the property of partial media in the models may be changed to simulate the variation of karst roadbed before and after grouting. The transient impact force was used to simulate hammer hitting vibration on the ground, and dispersion curves for ground test points in the two numerical models were analyzed comparatively. The research result shows that under the condition without karst cave, grouting leads to the wave velocity of dispersion curve to increase, while under the condition with karst cave, grouting makes the wave velocity of dispersion curve raise and the zigzag distortion of the dispersion curve before grouting disappear to indicate the same result as the field test.