In order to solve the problem that it is difficult to effectively compensate the error caused by the angle in ultrasonic ranging, based on the theory and method of function approximation, a compensation method of the error caused by the angle in ultrasonic ranging is proposed. Firstly, the propagation and incidence process of ultrasonic pulse are simulated. The simulation results show that the propagation speed of ultrasonic pulse is different under different ranging angles, which becomes the medium of error introduction. Then, the correlation relationship between the ranging angle and the error under the action of this medium is analyzed through experiments, the basis function model combination method is used to construct the ultrasonic ranging angle error model. Finally, aiming at the problem that the model independent variables (measured distance and ranging angle) must be known values, and error compensation cannot be achieved in practice, the measured value of ranging is taken as the variable of the iterative calculation, the model is taken as the relational expression of the iterative calculation, and a compensation algorithm of the error caused by the ultrasonic ranging angle is designed. The actual measurement verifies that the algorithm can make the average value of the ranging error less than 1. 1 mm when the ranging angle changes, which effectively compensates the error caused by the ranging angle and improves the accuracy of ultrasonic positioning.