In recent years, confocal microscopic imaging with charge coupled device (CCD) as a detector is a new method of confocal imaging. In this scheme, the lateral resolution of system is not only affected by the numerical aperture of the objective, but also the pixel of CCD, which is in the point spread function area of imaging and detection part. Using CCD instead of the pinhole and point detector of conventional confocal imaging, the synthetic equivalent pinhole of CCD pixel is chosen by different sizes of the point spread function area of a certain combination. The optimized synthetic pinhole is got by comparing the lateral resolution of system with different sizes of synthetic pinhole. By weighted subtracting of the image from different synthetic pinholes, subtractive imaging is realized and the lateral resolution can be enhanced. Experimental results show that when the synthetic pinhole is 0.8 times (8 pixel×8 pixel) of Airy spot diameter, the scanning image has higher lateral resolution and signal to noise ratio. When the image with the larger pinhole (10 pixel×10 pixel) is weightedly subtracted from the image with the optimized pinhole (8 pixel×8 pixel), the lateral resolution of subtractive image relative to optimized pinhole image with weight coefficient of 0.6 is improved by 21.7%. Using CCD as a detector can greatly reduce the complexity of the conventional confocal imaging system. By selecting the optimized synthetic pinhole and processing subtractive imaging, we can improve the lateral resolution of imaging.