Abstract: In order to avoid the influence of thermal deformation of machine tool on machining accuracy, and in view of the characteristics of high-speed mechanical spindle with large heat output and unbalanced heat in transmission chain. A real-time compensation method of spindle's thermal elongation based on SINUMERIK CNC system is proposed. A horizontal machining center is taken as the research object. The thermal elongation of the machine's spindle is detected by the spindle thermal deformation analyzer. The real-time changes of the tool in the directions of X, Y and Z are collected and the curves are generated. Five temperature sensors are laid out in the spindle system to collect the internal temperature of the spindle system in real time. The thermal error model of the mechanical spindle is established by using linear regression method. Combined with the synchronous function and temperature compensation function provided by SINUMERIK CNC system, the position of tool is compensated in real time and the machining accuracy of the machine tool is effectively guaranteed.