The main method to enhance the system capacity of OCDMA networks is coding user's data in both time and spectral domains. Based on the 1-D optical code-pattern and code-hoop,a new geometrical device is designed,called optical code-cylinder,to denote the wavelength-time 2-D optical signature codes,from which the scheme of correlation checking of 2-D signature code family is given. Then based on the optical code-cylinder,the analytical theory of maximum system capacity of 2-D OCDMA system is established in detail. The results from code-cylinder are concordant with thoses of Johnson bound of correcting code.So,the code-cylinder method is useful and convenient tool for the performance analysis of 2-D signature code.