The invention discloses a supporting leg for a child safety seat and a child safety seat. The supporting leg for the child safety seat and the child safety seat are characterized in that the supporting leg comprises a base and a strut assembly, wherein the base is supported on a car floor, and the strut assembly is arranged on the base; the child safety seat comprises a fixed seat; the supportingleg further comprises a piston rod whose upper end portion is fixedly connected at the bottom of the fixed seat; the strut assembly is provided with a cavity; a cement material is filled in the cavity; the lower end portion of the piston rod is located in the cavity and capable of being in up and down slidable arrangement in the cavity; the lower end portion of the piston rod is fixedly provided with a lower platen located in the cavity; when the child safety seat is subjected to an instantaneous longitudinal impact from above, the piston rod moves downward to cause the lower platen to squeezethe cement material in the cavity. The supporting leg for the child safety seat has the advantages of having effective buffering and energy absorption of the instantaneous impact force in the vertical direction when a vehicle is in a traffic accident, reducing the adverse effects of vehicle bumps on occupants while driving, reducing the risk of the occupants being injured, and improving the safety and comfort of rides.