Derricking device of flexible transmission is widely applied in crawler cranes, while its derricking speed hasn't been studied very well. In this paper, the kinematics model of derricking device is firstly established. Next, the dynamic analysis is done. A succinct method based on the load's prescriptive swing angle is put forward. The reasonable speed and acceleration of derricking device are determined according to the method. The adopted values provide a reliable basis for design and analysis. The study puts a way for the following work. All in all, it is innovative.