A cellular automaton method is presented to simulate rock failure. Force and displacement are taken as the basic state variables. Based on the basic mechanical laws vector updating rules are constructed

which overcomes the shortcomings of arbitrary decision of local rules and scalar variables. Based on this cellular automata model

rock failure process is simulated under uniaxial tensile conditions. And the influences of heterogeneity and sample shape on uniaxial tensile strength are studied. The results reveal uniaxial tensile behavior of rock and guide the uniaxial tensile experiments.