The invention discloses a blade mounting device used for a garden machine. The device comprises a mounting base. The top of the mounting base is provided with an X-shaped sliding groove. The X-shapedsliding groove is internally slidably provided with four sliding blocks, and the sliding blocks are corresponding in pairs. Sides of the four sliding blocks, close to each other, are provided with fixing clamping borads. One side of the top of the mounting base is provided with a first limiting block, and the other side of the top of the mounting base is provided with a second limiting block. Thefirst limiting block and the X-shaped sliding groove, and the second limiting block and the X-shaped sliding groove are arranged in a staggered manner. A threaded rod which is arranged horizontally isrotatably connected between the first limiting block and the second limiting block. One end of the threaded rod is provided with a handle, and the handle is on one side of the first limiting block, far away from the second limiting block. The outer side of the threaded rod is connected with two movable plates in parallel by threads. The device is rational in design, and simple in operation, and provides convenience for mounting trimming blades in different specifications, and installation is convenient, so that installation efficiency of the device is effectively improved.