Focus on the ultra-tight INS/GNSS integration, the NH code evasion method is proposed in BeiDou baseband signal process. An ultra-tight INS/BeiDou integration model based on vector tracking loop is built to analyze the coupling mechanism and control scheme between loop measurements and INS navigation data. Two control schemes are derived, including the relationship between code phase difference and the INS positioning error, the relationship between frequency difference and INS velocity error. A prototype based on BeiDou software-defined receiver and MEMS is designed and the model is tested.