Based on strained silicon metal-oxide semiconductor field transistor (MOSFET) structure, the distribution of surface potential is obtained by solving two-dimensional Poisson equation, and the threshold voltage model is built. According to calculation results, the dependence of threshold voltage on germanium content of relaxed Si1－βGeβ, channel length, voltage of drain, doping content of substrate and channel are studied in detail, and the influence of drain-induced barrier-lowering on scaled strained silicon MOSFET is obtained, which can provide important reference for the design of strained silicon MOSFET device and circuit.