Abstract: Theoretically, the junction frequency of each layer in an oblique ionogram formed by a particular circuit should be located in the leading edge of a backscatter ionogram which contains the circuit racially. However, the measured data show that there is always a mismatching between them. Based on the differences caused by different locations for transmitting and receiving of the backscatter sounding, the backscatter sounding group path is modified according to the radio wave propagation theory of an backscatter sounding system. Comparing the results after improving three directions from north to south, it indicates that the root mean square errors is improved by 12.2%, 12.4% and 12.8% respectively, which has a significant impact on the mode information fusion for the oblique and backscatter sounding.