Belonging to the field of position coordinate calculation methods, the invention specifically relates to a position coordinate calculation method for RPV ultrasonic detection incremental coded signals, and realizes incremental encoder real-time settlement of a multi-shaft linked inspection tool's probe terminal position. The principle is simple, the technology is mature, and can achieve precise position coordinate calculation of incremental coded signals. The method consists of six steps, and finally converts coordinate values into incremental coded signals and transmits the signals to ultrasound equipment.