As a new type of large mode area fiber ,gain-guided and index-antiguided (GG-IAG) fiber has been widely concerned.Ba sed on the GG-IAG fiber theoretical model,the formula of Nd³⁺ doped phosp hate GG-IAG fiber glass material was designed in this paper.The GG-IAG fiber preform was prepared by tube bar method.The Nd³⁺ doped phosphate GG-IAG large mode area fibers with different diameters (200－500μ m) were drawn at 530℃.The spectral parameters and gain performance of the GG-IAG fiber were tested.However,the gain performance is poo r due to the leakage loss of the optical fiber.In order to improve that,the effect of coating Ag film on the gain performance of GG-IAG fiber was studied.The experiments were based on the GG-IAG fiber with d ifferent core diameters,such as 130μm,160μm and 200μm respectively.By mag netron sputtering,a 200nm-thick Ag film was a pplied on the surface of the fiber cladding as a total reflection film,the pump light was bound to the optical fiber,thereby improving the pumping efficiency.The experimental results show that the Ag film has higher signal amplification effic iency than that without Ag film with the same core diameter.And the amplification efficiency of Ag coated fiber is 50%,41.88% and 24.33% respectively,while that of the unplated Ag film fiber is 26.87%,22.8% and 15.87%,respectively.It shows that the optical fiber surface coating can significantly improve the gain performance of GG-IAG fibers,and the results are of guiding significance for the application of GG-IAG fibers.