Abstract: Chirped fiber grating can be used in compensating fiber dispersion and compressing pulse.With the coupledmode theory,some parameters are analyzed, including grating length,coupled functions, chirped coefficient having relations with the reflectivity coefficient, timedelay character, dispersion and compression character. With the results , an Yb3+doped ultrashort pulse fiber laser is designed and an allfiber ring cavity with chirped fiber grating is brought forward. Comparing with the other structures of the nonallfiber lasers,the structure we designed is more efficient and has less power loss.