Abstract: Magnetic abrasive finishing, as a new surface finishing technology, has unique advantages in lapping the inner wall of slender tubes, but there are few CNC machine tools for magnetic lapping in the market. Aiming at the defects of traditional numerical control system applied to small machine tools, this paper designs the embedded software and hardware of numerical control machine tools based on STM32+FreeRTOS real-time operating system, and establishes a three-layer topological software system. The spindle speed servo control was studied, the spindle mathematical model was established through system identification, and PID parameters were set based on Ziegler-Nichols method. Taking biopsy needle as an example, a practical grinding experiment was carried out. The experimental results show that the grinding process of the machine is stable and the machining accuracy is high.