Based on the characteristic of a confocal microscope (CM) that the offset of a pinhole along an optical axis changes the axial intensity response phase, a novel tri-heterodyne confocal microscope is built up by dividing the CM measurement light path into three paths, and using three sets of focusing lenses, detectors and pinholes placed behind, on and before the focal plane to form three detection systems, thereby achieving the axial superresolution imaging and high Signal Noise Ratio (SNR) through pairwise heterodyne subtraction of three intensity signals with given phases received by the three detection systems and data processing. Simulation and experimental results indicate that the new tri-heterodyne confocal microscope reduces the full width at the half maximum of CM axial response curve by more than 50%, results in the significant improvement of CM anti-interference capability, and enables CM to be more suitable for high accuracy bipolar absolute measurement of 3D microstructures and surface contours.