This paper introduced a three-degree-of-freedom (3-DOF) photoelectric stabilized platform (PSP), and the Finite-Step-Integration (FSI) method was applied to analyze the kinematics characteristics. The motion process of the mechanism is segmented linearly, and the mathematical model of forward kinematics (FK) with iterative parameters is created and solved. The kinematic simulation is verified in ADAMS software, and the calculated results are compared with the simulation. The workspace of the PSP is analyzed to describe the working dimensionality characteristics. The results show that: the FK algorithm based on the FSI method has enough computational precision and can be efficient for the workspace analysis. This paper's research provides a good reference for the design and kinematics characteristic analysis of PSP.