Today，in more than 95% logging trucks, hydraulic system is adopted. Cable will be crawled when the cable running speed is less than 30 m/h, influencing reliability of test data. An analysis was made in view of the phenomenon that cable crawled. By simulation experiments and real use,a solution was proposed that ultralowspeed valve was added into the low pressure pipe from the motor to the pump in the hydraulic system which made the cable run stably under the speed less than 30 m/h. Then the stability and reliability of the collected data can be guaranteed.