A multi-point calibration method for the depth of a horizontal directional drilling guiding instrument comprises: maintaining a constant power output of a normal power transmitter in a specific power supply condition; selecting at least two depth calibrations; receiving a signal transmitted from a transmitter and an intensity of a signal at a depth calibration position by a receiving instrument; performing a signal shaping and an analog/digital conversion to the signal received by a signal receiving instrument; and entering the signal into a central digital signal processor, and performing a depth calibration by any compensation method to obtain a required measuring depth. The invention improves the accuracy of the depth measurement of the horizontal directional drilling guiding instrument by using a plurality of compensation methods to compensate any error caused by the electric fields and environmental noises and occurred in the depth measurement of horizontal directional drilling guiding instrument.