A rail type automatic fixed-point watering system comprises a humidity detecting module lightly buried in plant root soil, the humidity detecting module is connected to a data transmitter, and the data transmitter sends signals to a server in real time; rails mounted at the two sides of a plant and an agricultural machine capable of walking on the rails are further included, and the agricultural machine comprises a water tank and a water spraying system. A signal receiver is mounted on the agricultural machine, after the signal receiver receives the signals of the server, the signals are fed back to an agricultural machine control system to control the agricultural machine to walk and stop, and meanwhile the agricultural machine is controlled to spray water and stop water. The rails are elliptical rails surrounding the plant planting row. The agricultural machine is controlled to carry out watering on places with too low humidity by means of humidity detection, and the system is high in efficient, saves resources and achieves all-weather management.