Based on quantum mechanics, a tunneling current of uniaxially strained Si nMOSFET is bulit. The relationships between the tunneling current and device structure parameter, biased voltage and stress are analyzed. The simulation result is shown to accord well with the reported experimentalal result, implying that our model is correct. Our result is also compared with the result of biaxially stressed silicon nMOSFET, which shows that the current of uniaxially straining Si nMOSFET is lower than that of biaxially stressed silicon nMOSFET, and so uniaxial devices have advantages over biaxial devices. The model has a definite physical mechanism and it is suitable not only for uniaxially strained Si nMOSFET, but also for uniaxially strained Si pMOSFET,as long as changing the relevant parameters.