The agricultural irrigation system is closely related to agricultural production. Nowadays, the agricultural Internet of Things (IoT) irrigation system has some problems, such as low adaptability to the actual agricultural environment, no feedback processing, and a lack of better implementation algorithms. To solve these problems, this paper designs and implements the IoT irrigation system based on an intelligent path planning algorithm and designs and manufactures the agricultural irrigation robot combining the Internet of Things. The system transmits humidity information to the server through the soil humidity sensor, and performs path planning through an improved path planning algorithm. Irrigation robots carry out cruise irrigation, which is then collected by soil sensors. Bayesian theory has improved the path planning algorithm proposed in this paper. In the proposed algorithm, we use as much information as possible to achieve full coverage irrigation in complex agricultural environments. Besides, we raise the most significant risk to avoid the lack of inspections in some areas. Finally, we conducted simulation experiments and field experiments to verify the effectiveness of intelligent IoT irrigation systems. The experimental results show that the Internet of Things system can meet most agricultural irrigation tasks' requirements.