In order to solve the problem of insufficient bearing capacity of traditional flexible robots,a positive pressure driven variable stiffness elastic axis was proposed based on the principle of particle plugging.The variable stiffness mechanism of the elastic axis was analyzed,and an experimental platform was built based on the variable stiffness elastic axis prototype to analyze the influence of different factors on the elastic axis stiffness through experiments.The experimental results show that the stiffness of the elastic shaft increases 2.1 times compared with that without filling.The larger the airtight cavity of the elastic shaft ring is,the more particles are filled,and the stronger the stiffness of the elastic shaft is.The larger of the inner airbag tube diameter is,the stronger of the elastic shaft stiffness is.With the filled air pressure of 0 and 0.3 MPa, respectively, the elastic shaft stiffness of the frosting treated steel balls is increased 3 times, and the stiffness of the elastic shaft filled with ABS irregular shape is increased 4.3 times.