In order to find the cause for discontinuous moving problem of cable swing beam of launch tower, the machine and hydraulic subsystem of cable swing beam are tested with modern testing technology. With testing signal analysis processing, the dynamic characteristics of hydraulic subsystem and rack mechanism was researched. At last the reason of discontinuous moving of cable swing beam was found. Some improvement advices are given. The research result will be useful to improve the reliability and security of cable swing beam of launch tower.