Aimed at the problem of nonlinear timedelay in hydraulic control system of pump truck boom, a dynamically compensation method of timedelay was proposed which suitably applied in the structure of pump truck boom. The timeseries method was used to predict vibrating attitude for the pump truck boom in the next time period in advance, which based on the history vibrating displacement data of pump truck boom tip. The nonlinear timedelay in the system was compensated dynamically, and reliable feedback data were provided for the position control system of pump truck boom tip. Reference inputs in real time were provided for control system of position and speed of hydraulic valve controlled cylinder. Field experiment has verified the effectiveness of timedelay compensation algorithm in the aspects of improving smooth manipulation of pump truck boom and response speed for the valve controlled hydraulic cylinder.