Grey system is extended to probability stat. theory. Grey probability axiom system is expounded. grey probability density function and Grey reliability calculating method are studied. Then, stress-strength interference grey reliability calculating model and its whitening solution method are established. The program is worked out with Matlab5.3.1 language. Some examples are given, balance analysis is made for the general reliability design method and it displays that this model is accurate & feasible,and can be used to implement sensitive analysis and robust reliability design when their parameters are changed to effectively control design parameters.