As the geometric of suspension unknown, the combination of suspension K & C steering geometry test , angle and location of the kingpin axis are analyzed and deduced. According to the principle of four-wheel positioning,kingpin inclination and caster's initial value can be calculated; Through the analysis of the rotation of the wheel center round the kingpin axis, derive spindle offset and longitudinal kingpin offset algorithm; Then through these two offsets, as well as kingpin inclination and caster, kingpin offset and caster trail can be calculated.