Based on the concept of the information invariance of an optical system,the property of the high resolution of the reflective confocal optical sensor is discussed.The characteristic of point light source and point detector of confocal scanning optical microscopy caused by the end of this sensor makes the view field smaller,increases signal to noise ratio,improves the anti interference ability.Because of the special characteristic of high axis resolution,the sensor can be used in the precise measurement of surface profile,shape dimension and curve contour,which provides a suggestion for a great deal of dimensional measurement in small space.