The invention provides a variable-cross-section channel of a multi-stage cusped magnetic field plasma pusher, belongs to the field of cusped magnetic field plasma pushers, and particularly relates to a variable-cross-section channel of a cusped magnetic field plasma pusher. The problem that a gas working medium easily leaks from a wall surface of a straight channel of the existing cusped magnetic field plasma pusher is solved. The inner side wall of the ceramic channel of the plasma pusher is fixedly embedded with n ring-shaped bosses along the axial direction of the ceramic channel; inner side walls of the n bosses are cylindrical surfaces; inner side walls of axial sections of the n bosses are arch-shaped; and n is a positive integer. The section of the channel is changed by adding the bosses in the channel, so that the section of the wall surface of the straight ceramic channel of the plasma pusher is variable, the gas working medium can be sufficiently ionized on the wall surface, and the gas of the wall surface can be prevented from leaking, so that the secondary plume flow possibly existing in an exit is eliminated. The variable-cross-section channel is applicable to the cusped magnetic field plasma pusher.