The invention relates to a crank and crankshaft mounting structure for mopeds. The crank and crankshaft mounting structure for mopeds comprises a crankshaft and a crank and is characterized in that the end of the crankshaft, connected with the crank, is provided with a limit projection, the inner side of the limit projection is provided with a square part made on the crankshaft, the center of the square part is provided with a threaded mounting hole, the connecting end of the crank is provided with a square hole the same as the square part in shape, the inside of the square hole is provided with a channel concentric with the square hole, and a threaded connector matching with the threaded mounting hole is disposed in the channel. The crankshaft and the crank are locked and fixed through the threaded connector, and accordingly the defect that the traditional connection of left-hand and right-hand threads is inconvenient to recognize is avoided, errors in delivery are avoided, and installation needs no recognition. In addition, the crank and crankshaft mounting structure for mopeds has the advantages of simple structure, quickness and convenience in assembly, high bearing capacity, high universality, low cost, attractive appearance, high safety and the like.