An erbium-doped fiber nonlinear coupler(EDFNC),in which the coupling parameters could be controlled by the light were firstly proposed. By using the fusing-elongation machine to fusing together two Er³⁺-doped fibers,a 3 dB nonlinear coupler was fabricated for the signal light at 1550 nm. When changing the pump light at 980nm launched into one arm of the coupler,the propagation-constant difference between two arms of the coupler would be changed,and then the relative output powers of signal light from two arms would also be changed. Measuring the input pump power and two output signal powers of EDFNC,it obtained the experimental curve of the bar coupling ratio versus the pump power.The experiments showed that when increasing pump power from 0 mW to 20 mW,the variation of coupling ratios could reach to 40%. The theory simulation and the experiment results were well consistent.