This paper proposes a semicool temperature compensation algorithm based on the double exponential model of the transient temperature rise curve to improve the performance of the 3-D ultrasonic positioning system. The error model of the 3-D ultrasonic positioning system is derived and the importance of temperature to the positioning accuracy is demonstrated. Then, the double exponential model of the transient temperature rise curve derived by the difference principle is established through a dynamic system identification method. On this basis, the semicool temperature compensation algorithm is proposed, which includes the estimation of the initial time t₀ , the principle of the choice of parameter k . The effectiveness of the algorithm is verified by temperature measurement experiments. The impact of the ambient temperature on the algorithm is also analyzed qualitatively. In the end, the semicool temperature compensation algorithm is proved to be able to improve the performance of the 3-D ultrasonic positioning system by the comparison experiments respectively under static measurement of a fixed point and dynamic measurement of a fixed line.