Abstract: To propose a curve suitable for designing the conjugate cam tightening weft and establish the coordinate equations of the conjugate cam profiles tightening weft. Utilizing the information of the trigonometric curves and conjugate characteristics of the prime cam and the return cam, the methods of determining the conjugate cam profiles were established. The double simple harmonic motion of the tightening weft cam's follower and the mathematical equations of the cam were established. The double harmonic motion can be applied to designing the conjugate cam tightening weft. It lays a theoretical foundation for designing loom cam.