It has been proved by experiments that multi-level optical storage can be achieved by photochromic media. A theoretical model of optical crosstalk in photochromic multi-level storage is proposed, which is the basic of compensation and equalization in subsequent electrical system. This model is based on the normalized coordinates presented by Hopkins in the classical scalar diffraction theory and the superposition of Fourier optics and photochromic marks. The results of numerical simulation show that the crosstalk will decrease if the center distance increases, hence the crosstalk of adjacent track could be neglected if no track error. The cross term of the adjacent mark and unwritten disk is the main component of crosstalk. The crosstalk rate is approximately a proportion function of writing power, that is, crosstalk caused by high level photochromic mark is much higher than low level one. The experiment has well certified the theoretical model.