The mechanics of the potential well of buried channel charge coupled device (CCD) are described. By solving Poisson’s differential equations, a brief calculation of the optimum operating point and maximum charge capacity has been given. The effect factors such as the buried channel junction depth and substrate doping concentration on the CCD’s optimum operating point and maximum charge capacity are analysed. According to the theoretical calculation, the charge capacity of the 6000 pixel linear CCD designed by our group is 4643 e/μm2.