Precise planetary gear speed reducer with adjustable transmission ratio

The invention discloses a precise planetary gear speed reducer with an adjustable transmission ratio. The precise planetary gear speed reducer with the adjustable transmission ratio comprises a shell, an input shaft, a speed reduction output shaft and a planetary speed reduction mechanism, wherein the input shaft and the speed reduction output shaft penetrate through two ends of the shell; the planetary speed reduction mechanism is in transmission connection with the speed reduction output shaft; one side, located in the shell, of the input shaft is provided with a first switching gear and a second switching gear which are in fixed-axis rotation; a joint sleeve is arranged between the first switching gear and the second switching gear; an annular groove is formed in the outer contour of the joint sleeve; synchronous rings are arranged at the positions, located at the two ends of the joint sleeve, of the outer contour of the input shaft; annularly-distributed splines are fixedly connected to the positions, loc