In the MLS airborne receiver, the C-band RF channel mix the signal into an intermediate frequency. IF signal is fed into the post-processing through the Analog IF filter. The calculation phase information is influenced by Analog IF filter amplitude and phase characteristics, especially the phase characteristics. Reasonable recognition evaluation of the influence of Analog IF filter to the system phase is the basic of design and assess of Analog IF filter. In this paper, the processing theory of the MLS airborne receiver dealing with phase information is introduced. Phase information influenced by Analog IF filter amplitude and phase characteristics is presented by the system perspective and a reference for the design of airborne receiver analog IF filter and the system is given.