Gas flow valves are widely used in pneumatic field. The technology of valves, such as butterfly valves and ball valves, combined with valve positioner mode is mature, and the prices are reasonable. But there are some disadvantages like nonlinear relationship between the opening degree of the valve and flow area, low positioning accuracy, lack of repeatability and so on. A new rotary flat flow valve with linear characteristics was proposed. The nominal diameter was 50 mm. With good repeatability, it can overcome the above disadvantages on the whole. It can achieve the linear regulation of flow from 0% to 95%. A special shaped curve was designed for the valve plate to achieve the linear relationship. And a decelerating stepper motor was used to drive the valve plate to ensure the accuracy and repeatability of valve. It can also quickly adjust the valve plate to any position. The function of the curve of valve plate was deduced with cut-and-fill method. Then a special plane-rotation seal structure was proposed to ensure the plate seal. The computational fluid dynamics method was employed to simulate the internal fluid field of the valve at different opening positions. Finally, detailed simulation and experimental study were carefully carried out to verify the design and performance of valve. Both theoretical calculations and experiment results showed that the linear correlation coefficient was greater than 0.99. Experiment results at different positions showed that the flow repeatability of the valve was better than 0.26%. Although the performance of the new structure valve had been verified, the reliability of the special seal and working lifetime of the rotary flat valve were pending to be proved in the future work.