A seven-level adjustable reciprocating type electrorheological fluid damper mainly comprises a positive-pole conducting wire, a negative-pole conducting wire, a positive-pole piston cylinder cover, a negative-pole piston cylinder cover, positive-pole conducting rubber, negative-pole conducting rubber, a piston rod, an insulating piston cylinder, a positive pole, a negative pole, a backflow control path, a small piston, a middle piston, a large piston and electrorheological fluid. The positive-pole conducting rubber and the negative-pole conducting rubber replace sealing materials and play a role in sealing and conducting. Installation forms of the small piston, the middle piston and the large piston are determined by borne damping force, wherein when the damping force is large, stress is not clear, and movement speed is high, the dual-piston or three-piston form is adopted; when the damping force is small, the single-piston form is adopted. The backflow control path replaces a throttling control valve, no external electric field exists, the electrorheological fluid bears the force and flows between the positive pole and the negative pole through the backflow control path, and the seven-level adjustable reciprocating type electrorheological fluid damper is a hydraulic damper; when an external electric field is applied and shearing efficiency is high, apparent viscosity of the electrorheological fluid of the backflow control path changes, the section area of the backflow control path becomes smaller, the backflow control path is even blocked completely, and the electrorheological fluid effectively controls an engineering system by proving shearing force and extruding force.