Abstract: This article simulates the movement of the spring simple pendulum by the starting value with various recursion methods, and the direction of motion of the pellet is divided into transverse direction and radial direction. The increasing of the initial angle can affect the rule of periodic motion in radial direction, and the change of the stiffness coefficient can affect the rule of periodic motion in transverse direction, hut the great stiffness coefficient also can affect the scope of periodic vibration in radial direction, so the pellet will make the periodic sine change movement in transverse direction and radial direction by choosing the small angle and the appropriate stiffness coef- ficient, and coupling influence of the movement of the pellet is very little in two directions.

Key words: simple pendulum with variable length, spring simple pendulum, transverse direction, radial direction, periodic motion