The initial alignment is one of the key technologies in Strapdown Inertial Navigation System（SINS）. The conventional alignment model was established by adding the disturbance of state vector in the ideal navigation equation. It is only used in the case of small misalignment angles and can't be applied to large misalignment angles. Based on the foundation of other nonlinear models and taking every influencing factor into account, the nonlinear model has been established when the initial warp angles are arbitrary misalignment angles and the relationship between the arbitrary misalignment angles nonlinear models and the small misalignment angles linear models has been analyzed. Then under the condition of static small misalignment angles, the simplified alignment models have been derived and a state evaluation to the models has been assessed by using Kalman filtering method. The calculating result indicates that the good state constringency can be realized. At the last part, other initial alignment of nonlinear condition is also discussed.