Abstract: The main reason that casing falls to the hole by breaking off thread is casing thread quality can't reach the criteria, and the management of casing running into the hole is not strict. When handling casing of big size fish accident, it is very difficult to find out ready-made fishing tool to match it. Operator needs to process fishing tools by himself according to the analysis of the problem. The reasonable choosing to the method of handling casing fish can shorten handling time of the accident effectively, and minimize economic loss of the accident. This article introduces several handling methods of casing fish of big size. Aiming to the different handling method, the article introduces each tool of the structure, the work principle and the usage conditions and methods respectively. These handling methods have definite reference value to handle the same kind of accident in the future.