In this thesis, the main goal is to estimate the minimum separation between each micro-hologram in three dimensions during holographic data storage. First, we analyze the two counter-propagating Gaussian wave when recording, we use the ray trace rule to determine the Gaussian beam’s waist size and location inside the medium, and then to check the two Gaussian waist is overlap or not after move the medium. We use Born approximation to analyze the diffracted wave. In reality, the observation plane and the material is separate in two different medium that will cause the refraction effect. So modify the form of the diffracted wave vector is important in this thesis. Based on Born approximation, we fine the characteristic of unit and multilayer recording. Finally, we determine the noise-to-signal ratio to decide the minimum separation in three dimensions, and further to analyze the storage capacity.