The selection of landing site is one of the vital steps for the Martian landing and roving mission. Both the scientific objectives and the engineering constraints should be considered. The engineering constraints are more important for the Martian landing mission due to the high risks in the process, which are mainly related to the surface characteristics of the landing sites, mission trajectory, atmosphere, etc. The surface characteristics include local elevation, slopes and relief, rocks distribution, dust thickness, sunlight and thermal constraints that can affect the EDL safety and the rover mobility. At first the engineering constraints are listed out and sorted in this paper. Then the analysis model based on fuzzy algorithm is set up, and the index for evaluating the suitability of different landing sites based on fuzzy inference is proposed. Finally, the method is validated based on the landing sitts of ExoMars 2020 mission.