The microstructures of MTG YBCO near 211 phase clusters inside the sample are studied by means of transmission electron microscopy. The results indicate that crystal defects around 211 phase are closely related to the distance between 211 particles ( d(211)). With the decrease of d(211), the twin spacing increases. Simultaneously, the thickness of the twin boundary decreases. When d(211) is less than 0.51 mu m, there are almost no defects between 211 particles. According to the established crack model, the mechanism of the appearance of a defect-free-zone is explained. The relationship between d(211) and Jc is discussed in this paper.