Unconventional oil and gas resources is very rich in China, and one of the important replacement resources. Industrial production oil and gas flow is mainly obtained through large-scale volumetric fracturing because its compactness reservoir, During the fracturing process, the casing has complex stress change characteristics, and the casing deformation is becoming more and more serious. At present, the understanding of the characteristics of the inner and outer walls of the casing, perforation clusters and intervals is not clear. Therefore, based on the characteristics of fracturing, a numerical simulation method is proposed to simulate and verify the fracturing parameters of typical casing change wells. The results show that: 1. In the fracturing and flowback stages, stress concentration occurs at the perforations, but the stress gradient changes little; During flowback, a high stress concentration is formed between the casing section between perforation clusters and the outer wall in the direction of perforation coaxial line, which is in danger of oval deformation; In the transition section from perforation section to perforation cluster section, there is a sudden inflection point of equivalent stress, which first decreases and then increases sharply in fracturing stage, and then increases and then decreases sharply in flowback stage. During flowback, the shear stress concentration in this section reaches the peak, which is prone to shear failure and casing dislocation. 2. In the fracturing stage, the cement sheath not only forms stress concentration at the perforation hole, but also has high stress distribution in the axial direction of the circumferential section of the cement sheath in the perforation cluster section, resulting in a certain degree of damage to the cement sheath. During flowback, the damage degree of the cement sheath is strengthened and the casing damage rate is high. 3. Under the condition of the same fracturing flow rate, properly increasing the length of perforation clusters, shortening perforation clusters spacing and fracturing sections spacing can effectively improve the safety of Casing. It is recommended that the length of perforation clusters of 51 / 2in P110 Casing in STH M56 is 1.5-3.0 m, the perforation clusters spacing is less than 10 m and the sections spacing is less than 30 m.