Abstract: through the long-term use of CA series horizontal lathe, it is found that there are design defects in the connection mode between spindle and chuck, so the structure design and connection mode improvement of spindle are carried out with CA6140 horizontal lathe as an example.After preliminary analysis and research, three improvement schemes are determined, and then through comparative study, the most reasonable and scientific improvement method is finally determined.Through 3D design and modeling, machining and production, on-site debugging and installation methods, this repetitive problem is finally successfully solved.After several tests, the machine tool runs more safely and stably, and the service life of the machine tool is greatly improved.