The evolutionary dynamics of psychological contract is characterized by uncertainty，nonlinearity，and catastrophes，thus it is modeled by stochastic cusp catastrophe theory to analyze the dynamics of fulfillment—breach on psychological contract．A behavioral variable ( i．e．，perception of psychological contract) and independent control variables ( i． e． ，personality and organizational context) are introduced．This paper is the first attempt to fit a cusp catastrophe model to the data by cuspfit software．The conclusions are that: 1) The organizational context，as a normal factor，and personality，as a splitting factor，play important roles in the catastrophe of psychological contract simultaneously; 2) There are two different kinds of discrete changes on psychological contract: turbulent sudden jumps and structural catastrophes; 3) There exist turbulent sud_x005fden jumps because of external disturbance when the control variables are in the bifurcation set，while structural catastrophes will result from self-organization when they cross the border of the bifurcation set; 4) The existence of hysteresis can explain why a psychological contract could not be easily repaired once it breaches．