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The varying speed support for continuous-flow left ventricular assist device (CFLVAD) is a feasible solution to improve blood flow pulsatility in patients. This study aimed to design a pulsatile varying speed controller (PVSC) for CFLVADs and test the PVSC in vitro. Based on the pulsewidth modulation (PWM) speed regulation method, the basic principle of CFLVAD pulsatile varying speed was elaborated in detail. The PVSC was designed and manufactured by combining software and hardware. The in vitro flow loop rig was built as the test platform for PVSC. Constant and varying speed experiments were designed to test the feasibility of PVSC. The blood flow pulsation experiment was designed to study the control factors affecting blood flow pulsatility. The experimental results showed that the designed PVSC could control the rotary pump to operate reliably in both constant speed and varying speed modes. Also, the mean pump speed played a role in regulating the mean aortic pressure and flow, and the pump speed amplitude and the modulation frequency jointly affected the blood flow pulsatility.