Abstract: To effectively simulate the spring load-bearing and failure states, and to reveal the mechanical performance of vehicle bogie primary steel spring and the impact of primary steel spring fracture on vehicle dynamics performance, taking the primary steel spring of an EMU (electric multiple unit) as an example, a discrete model method spring refined modeling of spring mass-parameter vibration is adopted. The theory and method of spring fine modeling are introduced. According to the actual spring fracture cases, the static and dynamic load-bearing law of EMU primary steel springs in different positions is analyzed. The vehicle dynamics performance of EMU train passing straight and curved sections under different failure conditions are simulated and analyzed. Research results show that compared with outside spring group, the static loads of the inner and outer ring springs of inside spring group are greater, and the inner ring spring affords only about 1/2 of the outer ring spring load; in the range of 2045 Hz for dynamic load frequency, the dynamic loads of the axle box inner spring are greater than the outer spring; the loadbearing condition of the outer ring spring on the axle box outside is the worst in the case of over-crush, and the outer ring spring is 1.2-ring away from spring bottom, the spring under over-crush condition will contact the bottom ring and the spring contact load reaches over 3 kN. When a single primary steel spring fractures, there′s little impact on vehicle stability, but the vehicle safety condition would deteriorate, especially when the fracture happens at the spring middle part, the derailment coefficient and wheel load reduction rate of the vehicle increase significantly.