This paper presents the resent advances in our research on ultrahigh resolution laser confocal microscopy to further improve the accuracy of non-contact 3D measurement of micro-structural dimensions and profiles at the level of micron/nanometer with emphasis on ways and means to improve axial and lateral resolutions. A scan measuring technique based on differential confocal microscopy is developed using the difference in the distribution of the scanning spot on near and far confocal planes by keeping the detectors off-focus at equal distance before and after the conjugate image plane of the scanning spot. This differential confocal microscopic scan measuring technique can be used to double the measurement sensitivity and obviously expand the linear range to improve the axial resolution, and to locate the tracking zero point at the center of the linear range with the highest sensitivity to achieve the bipolar tracking properties. In addition, this new technique can be used to effectively suppress the light source intensity drift and detector electronic drift and noise to improve the S/N ratio. The differential confocal detection technique can be combined with the optical superresolving filtering technique to improve both lateral and axial resolutions, and the confocal detection technique based on micro optical arrays has a very promising potential application for improving of detection efficiency.