The paper introduces the composition and characteristics of GBS-55 horizontal directional drilling machine. According to the operating characteristics of main mechanism of GBS-55 horizontal directional drilling machine and the actual working conditions, the hydraulic system was designed. The main features of this hydraulic system were analyzed and based on the design parameters of the hydraulic system, the design calculation and selection of the major hydraulic components were carried out. The practical application shows that this hydraulic system is stable and efficient with strong load adaptability.