The invention provides a worm-gear transmission system of a reel irrigator, and belongs to the field of agricultural water-saving irrigation. The worm-gear transmission system comprises a transmission body, a first-grade worm-gear power train, a second-grade fixed axis gear train, a third-grade fixed axis gear train, a manual recycling gear train and a gear shifting device. According to the worm-gear transmission system, through control of the position of a shifting fork in the gear shifting device, the worm-gear transmission system achieves gear 1, gear 2, neutral gear and manual recycling speed regulation modes; a brushless direct current motor replaces a water turbine to output power, so that the power performance of a prime mover is improved; and worm-gear transmission replaces parts of straight toothed spur gear transmission, so that the transmission ratio of the reel irrigator is increased, the transmission efficiency of the reel irrigator is improved, the size of a transmission is decreased, and the technical problems that under the low-speed operation condition of a traditional reel irrigator, the water turbine is insufficient in power performance and low in efficiency, a traditional transmission has multiple grades and is low in transmission ratio, large in size and low in efficiency, and the like are solved.