Abstract: When some three-axis electro-optical reconnaissance platform works, it needs using light beam to circumrotate on platform surface. In order to calculate the attitude of the light axis during platform working, the quaternion algorithm and coordinate transformation algorithm were adopted to solve this problem. Simulation results show that the two methods can both get better effect;however, the coordinate transformation algorithm has enormous computation and bad real time feature for using lots of trigonometric functions,while the quaternion algorithm has few trigonometric functions which is more easy for practice applications.