In order to solve the problem that the pressure and angle changes are difficult to predict in the process of hydraulic crane operation, the model of hydraulic crane movement control based on an assumed mode was proposed. The structure of the hydraulic crane was introduced. The Lagrange theorem was used to model the moving arm of a hydraulic crane, and the dynamic equation of the crane was deduced. Assumed that the translational link was approximately a single beam, the deformation of the telescopic boom of the hydraulic crane was studied. The pressure of the hydraulic crane actuator and the rotation angle of the boom were simulated by MATLAB. The simulation results were compared with the actual measured values. The results show that the simulated pressure change value of the hydraulic crane actuator and the change value of the suspender rotation angle are close to the actual measurement values, which can make a good prediction of the pressure change and the suspender rotation angle change in the actual work. The hydraulic crane motion model based on the assumed mode can effectively simulate the pressure change and angular displacement change caused by the crane arm motion.