Abstract: In order to improve the load carrying capacity, variable-stiffness performance and stability of the soft driver, a fiber-particle jamming based soft driver is designed by combining the advantages of the pneumatic network driving structure and the jamming based variable-stiffness structure, and its variable-stiffness mechanism is studied. Firstly, the structure of the fiber-particle jamming based soft driver is designed by using the better stability of fiber jamming and the stronger variablestiffness performance of particle jamming. Secondly, the fiber-particle jamming based variable-stiffness model is established based on the Hertzian theory and the principle of virtual work to theoretically study its variable-stiffness mechanism. Finally, the prototype of the fiber-particle jamming based soft driver is manufactured to carry out the stiffness test, the comparative test of variable-stiffness performance, and the stability test. The results of stiffness test show that when the fiber radius is 1.25 mm and the particle radius is 0.3 mm, the maximum stiffness of the fiber-particle jamming based soft driver is 0.1825 N/mm. The results of comparative test of variable-stiffness performance show that the variable-stiffness performance of the fiber-particle jamming structure is increased by 88.05% compared with pure fiber jamming structure, and 26.73% compared with pure particle jamming structure. The results of stability test show that the stability of the fiber-particle jamming based soft driver is 67.43% higher than that of the pure particle jamming mode. Compared with the particle jamming and fiber jamming based soft drivers, the stiffness, variable-stiffness performance and stability of the fiber-particle jamming based variable-stiffness soft driver are all highly improved.