A swinging harmonic error occurs between the measured distance of the indirect time-of-flight (ITOF) camera and the real distance due to the nonideal factors of the optical waveform of the laser transmitter and the tap response of the imaging sensor. The harmonic error can interfere with the accuracy of distance measurement. This paper analyzes the causes of harmonic error in ITOF cameras and clarifies the relationship between the harmonic error period, ranging period, and number of pixel taps. Based on triangular series fitting, this work proposes a method to correct such harmonic errors in a short calibration range and a large calibration step, which improves the calibration efficiency. The effectiveness of the proposed method is verified through 66.67 MHz 3-tap ITOF camera ranging experiments. The experimental results show that the average distance measurement accuracy of the principal point pixel is 2.5787 mm, while the average plane fitting error in the plane distance measurement is 4.3876 mm. Thus, the findings emphasize that the proposed method can effectively reduce the harmonic errors in distance measurements using ITOF cameras.