Sonic drill rig is high-end soil sampling equipment. The hydraulic top-drive head of the drill rig generates high-frequency exciting forces to drive the drilling tool to overcome the resistance of shallow formation so as to make the formation around the drilling tool liquefied locally， and then quickly obtain high-quality undisturbed samples from formation. Based on the main design parameters of the 50m sonic drill rig， the open hydraulic system was selected to simplify the oil circuit structure of the system through analysis of the hydraulic system design of the drill rig， The hydraulic system adopted the control plan of the main hydraulic circuit and the auxiliary hydraulic circuit， where the main hydraulic circuit drives the vibration， rotation and feeding of the top head， and crawler walking； the auxiliary hydraulic circuit drives the leveling of jack legs， putting up and putting down， and sliding of the mast. The parameters of the hydraulic system were designed and calculated with the working pressure of the hydraulic system of the drill rig selected as 21MPa， and the total flow of the main hydraulic circuit calculated as 320L/min. Therefore， the engine was determined. Then the hydraulic system was installed and debugged， and the drill rig was tested. On this basis， the sampling application and promotion of the drill rig， includes sampling with large diameter double-layered tube and split-tube and samling in complex formation， was carried out with good sampling results. The hydraulic system of the drilling rig is stable， safe and reliable， with beautiful hydraulic line layout， flexible and convenient operation， which can meet the requirements of engineering application.