A digitisation scheme of multi-mode navigation receiver is presented to solve the incompatibility of various navigation mechanism. In the scheme, the multi-mechanism navigation signal is analysed and processed using only one FPGA (Field Prognammable Gate Annay) after AD (Andlog to Digital) sampling of the intermediate frequency signal, at the same time, the size is reduced greatly. This paper mainly analyses the frequency planning, sampling frequency, the analog front-end circuit, gain distribution and the AGC circuit of the intermediate frequency digitised receiver based on Software Defined Radio. The analysed data indicate that the scheme is feasible.