To solve the transverse vibration problem of the time varying configuration of the ADAM type mast in deploying process, the stiffness of ADAM type mast is deduced on the basis of the equivalent continuum model, and then the governing equations of transverse vibration during deploying process are yielded based on Hamilton principle. Utilizing the weighted residual method, the partial differential government equations are transformed into ordinary differential equations, and the equations are solved numerically by using Runge Kutta method. The calculational results show that transverse amplitude of the mast end decreases in retracting process. It means that retraction process is reliable and safe. While in deploying process, the transverse amplitude of the mast end increases with increase of deployment length and tip load of the mast. Effect of deploying velocity on the amplitude could be ignored if lock impact isn’t taken into account. If periodic lock impact is considered, the amplitude will increase obviously, and the deploying velocity should be limited to decrease the transverse vibration. The conclusions could be applied in the control of on orbit deployment of the ADAM type mast.