Abstract: A new method to estimate the F layer second-hop propagation mode based on the first-hop on oblique ionograms is developed. The method is compared with the smart short wave ray tracing technique and validated by real oblique ionograms. The difference between estimation and the real results is analyzed. Both the simulation and the experiment results prove that the method is comparatively accurate in obtaining the ranges of group path and frequency of F layer second-hop mode and is beneficial to identify the propagation modes of different frequencies on oblique ionograms. It can be used as a priori and assistant information for the intelligent identification technique of oblique propagation modes.