Sensors like CCD used to record two-dimensional information have many applications in scientific researches. The sampling digit of CCD is a very important index related to the signal quality, price and data transmission speed. The aperture-coefficient of CCD is also an important factor which could influence the signal quality. Using numerical simulation method, the sampling digit and diaphragm are discussed based on aspects of standard deviation and power spectrum, and the best CCD work-state diagram is achieved. The results show that 4-bit and 6-bit CCD could easily produce a large signal distortion, while 8-bit CCD only with proper operation can have the same effect as 12-bit CCD to reflect the real signals without signal distortion. The optimal CCD work-state diagram derived from the simulation results, provides certain theoretical guidance for data acquisition using CCD and has some practical significance.