The synchronization of two same fractional-order chaotic systems with control constrain is investigated. Firstly, based on the linear control theory and adaptive control theory, an adaptive proportional switching control scheme is designed without eliminating the nonlinear part. Then, considering the constraints of the controller, the linear part of the controller is improved using the soft variable structure method which can provide infinite sub-controllers. The soft variable controller is designed for dealing with the control constrain and optimizing the linear controller. At the same time, the stability of the error systems is proved based on the fractional-order Mittag-Leffler theory. Giving consideration to the stability and the robustness of the system, the adjustment time is shortened and the chattering is effectively suppressed. Finally, by using the designed controller, the synchronization of the fractional-order Chen chaotic system is realized. The numerical simulation results show the effectiveness and feasibility of the designed controller. The advantages of the soft variable structure method, which is used in the control of synchronization of fractional-order chaotic systems with control constrain, are verified by comparing the simulation of the two controllers.