Considering the gap between the wheel and axle, the dynamic model of a three-piece and gauge-changeable truck was established, and the running performance of the vehicle and the wheel-rail contact characteristic of LM tread on both the standard and broad gauge tracks were investigated. The LM tread with gauge 1435 mm and 1520 mm, the rail inclination 1/40 and 1/20, and the standard and worn rail profiles were selected for parameter analysis. It was found that the compatibility of LM tread for two kinds of rail inclinations is good, but it is sensitive to the change of the bottom slope after tread wear. Moreover, the LM tread is sensitive to the transverse gap the wheel and axle on the standard line, but insensitive on the wide rail line. The transverse and rotational gaps lead to a reduction in the critical speed of the vehicle, which are recommended to be selected within 0.6mm and 0.5mrad, respectively. However, the gaps do not affect the safety and smoothness of the vehicle operation, and the dynamic performances of the vehicle on the standard and wide rail lines are almost the same. During the operation of the gauge-changeable vehicle, both the transverse force and longitudinal creep force between the wheel and rail lead to dynamic changes of the transverse and rotational gaps. Finally, the normal distribution statistics of the axle-gap and wheel-rail loads were conducted, which indicated that the axle-gap load is equal to the wheel-rail load.