An analytical model for the subthreshold current of fully depleted strained -SOI MOSFET was developed by solving the two-dimensional (2D) Poisson equation and the conventional drift-diffusion theory. Model verification was carried out using the 2D device simulator ISE. Good agreement was obtained between the model's calculations and the simulated results. By analyzing the model, the dependence of current on the strained Si layer strain, thickness and doping was studied. This subthreshold current model provides valuable reference to the FD-SSOI MOSFET design.