Abstract: Optical data storage based on a two photon process is one among the most promising approaches for realizing high density three dimensional data storage. In order to improve the conventional single beam two photon bit by bit writing methods, a novel method viz.that of single lens, two beam, two photon bit by bit writing is proposed. The key point of the method is an annular divided objective lens used in the laser beam focusing system. In order to illustrate the efficiency of this new method, a series of numerical simulation experiments for calculating the intensity distribution of two photon recorded signal in longitudinal direction have been carried out. The simulated results showed that, by properly regulating the intensity ratios of the two input lasers, a desirable two photon recorded signal resolution can be achieved in the longitudinal direction. The new method may be used in high density three dimensional optical data storage.