In order to study the effect of micro-cracks on the damage growth, the different field enhancements of the Hertzian micro crack are investigated by varying its angle, width, and depth. Simulation results show that the most harmful cracks are those with inclination angles from 20.9° to 45°, and the cracks with an angle less than 45° and larger than 48.2° are also harmful, but the cracks with inclination angle of 45° are the least harmful. Increasing the depth of the Hertzian cracks will lead to their field enhancement factors increasing with a quadratic relationship. However, increasing the width does not make it essential to the increase of its field enhancement ability. The development of micro-cracks can be approximated by increase its depth and width, so the development of cracks will lead to the increase of its light field modulation capability, and also to its damage growth rate to accelerate, following an exponential law.