Abstract High-speed downhole transmission technology plays an important role in measurement while drilling (MWD) and logging while drilling (LWD) systems, where the continuous wave mud pulse transmission method is currently the most advantageous method for wireless downhole transmission. To increase the production rate, transmission distance and testing intensity and to decrease the ground detected difficulty of continuous wave mud signals, the valve orifice must be optimized to satisfy the requirements for the continuous sinusoidal pressure output. In this study, an improved arc-fillet-line triangular valve orifice is designed based on a general line triangular valve orifice according to the relationships between the fluid differential pressure of a thin-walled cutting edge and the fluid flow area and between the correlation coefficient of the theoretical pressure difference and standard sinusoidal signal. The improved orifice is designed by calculating the variation between the flow area and relative rotation angle of the rotor to the stator through the established polar coordinate equations. The optimized valve structure is simple and easy to machine, and highly similar sinusoidal pressure wave signals can be achieved during practical operation to meet the requirements of the instrument design.