As a key component of heavy gantry CNC machine tools, the accuracy reliability of segmented beam has an important influence on the machining accuracy reliability of machine tools. First, the dynamic response analysis was carried out by using the finite element model of segmented beam considering the influence of joint surface. Then, based on the stressstrength interference theory, a processing reliability model of segmented beams was proposed. Finally, the above model was used to study the process reliability analysis under different cutting parameters and different tool parameters, and the engineering solution is given, which provides a basis for improving the machining accuracy and retention of heavy CNC machine tools.