Fiber large diameter end-cap splicing is one of the key technologies to increase energy transfer in fiber up to kilowatt. In order to achieve fiber large diameter end-cap splicing, the splicing mechanism of fiber end-cap is analyzed theoretically. A system of fiber end-cap splicing is designed and built based on CO2 laser, and the method and processing of fiber large diameter end-cap splicing are investigated and implemented. The continuous wave laser up to kilowatt is transferred successfully by the fiber that is with spliced large diameter end-cap.