With remarkable advantage of comprehensive cost, multicrystalline based photovoltaic module products become the most competitive and widely used PV products. A strong correlation was found between crystal defects of multicrystalline silicon and the cell efficiency thereby. The defect density at the bottom and top brick is very high, as a result, the corresponding cell efficiency is low (14.5~15.5%). The cell efficiency of the wafers from the middle position of brick is high (16.5~17.5%) due to the low defect density. However, different kinds of defects exert different influence on the cell performance. For instance, some stable defects (such as dislocation) will survive at the final cell, and some other defects (such as interstitial metal impurities) are removed during the cell process.