In order to solve the problems of complex multi-degree-of-freedom robotic arm structure and high coupling control, a three-dimensional robotic arm system in polar coordinates is designed in this paper. Due to the traditional mainstream control algorithm being prone to rapid changes in stepper motor speed, resulting in damage to the mechanical structure of the system, we propose a strategy for robotic arm control based on stepper motor and distance-speed curve. The distance-speed curve stepper motor control algorithm establishes the maximum operating speed curve according to system design requirements, mapping the target distance parameters to the speed curve to achieve speed control. The experiments prove that the three-dimensional robotic arm in polar coordinate reduces the complexity of the system and improves the reliability and practicality of the system.