This paper describes the results of X-ray study of imperfection in the single crystal of large area synthetic fluorophlogopite. By using X-ray Laue method, it is showed that in synthetic mica there is a greater degree of one-dimensional disorder, and therefore there are a number of disarranged regions of stacking sequence and their boundaries. The X-ray diffraction topography method shows that most of sub-grain boundaries and dislocations originate from the seed and run normal to the growth surfaces. The density of crystal defects in the region near the crystal surface is greater than that in the center. The difference in the distribution of defects between synthetic mica and natural mica was investigated. The relationships between defects in synthetic mica plate and their performances as used to construct condenser were also studied and discussed.