A pump-blockage-preventing structure for a concrete pump comprises worm drive structures, spiral blade propulsion structures, a main oil cylinder spindle sleeve and a concrete cylinder spindle sleeve. The worm drive structures adopt common worm drive means. External thread segments on piston rods and internal threads on nuts form a screw pair. The worm drive structures which adopt single-line threads and do not self lock have the characteristics of transmission reversibility. The spiral blade propulsion structures are fixed on the outreaching ends of the piston rods located inside a concrete cylinder along a helix by adopting a plurality of blades. When a piston in a main oil cylinder is driven by the hydraulic oil in the main oil cylinder to move horizontally, the piston rods achieve forward movement and forward rotation or reverse movement and reverse rotation. When the piston rods perform forward movement and forward rotation or reverse movement and reverse rotation, the spiral blade propulsion structures which are fixed on the outreaching ends of the piston rods along the helix by adopting the blades then generate assistant thrust or assistant suction force. The pump is then prevented from being blocked. The structure which is simple and effective lowers the pump blockage frequency, alleviates the labor delay problems due to the blockage of the pump and improves the working efficiency.