The invention relates to a production method of low-phosphorous-content gear steel for an automobile gearbox. The production method comprises the process flow including converter smelting, LF+RH refining, continuous casting, hot rolling and rolling. According to a converter technology, dual-drag smelting is adopted, steel ladle slag is improved while the quantity of slag discharged out of a largeladle is decreased, and the content of FeO in large ladle slag is controlled to be equal to or lower than 1.5wt%. According to the LF refining working step, final slag is subjected to refining operation with the high alkalinity and the low calcium-to-aluminum ratio, and in the process, aluminum wire making precipitation deoxidation is used in cooperation with slag top calcium carbide diffusion deoxidation. According to RH, ferrotitanium is added in the later period of high-vacuum circulation, and the soft blow time after calcium treatment is longer than or equal to ten minutes. Protective casting is carried out in the whole process of the continuous casting step, the problems in tundish oxygenation and working procedure recarburization are solved by adopting a covering agent with the low content of ferrous oxide and a low-carbon slag absorbing agent, and a casting blank enters a pit for slow cooling after being discharged out of a production line. With the production method of low-phosphorous gear steel for the automobile gearbox, the technical problem that the gear steel for the automobile gearbox is relatively high in phosphorus content, unstable in ingredient, wide in bandwidthrange of hardenability, and the like is solved.