Abstract: In this paper, the nonlinear effect of Rijke thermoacoustic oscillation is studied. Two reasons which cause the nonlinear effect are given. They are the nonlinear thermoacoustic mutual relation and the nonlinear radiating impedance of sound wave at end of the Rijke tube. The results of nonlinear effect are also directed by calculating the growth rate of sound wave in the tube and experimental analysis of the spectrum of sound wave. It's found that nonlinear effect stabilizes the sound wave and cause the production of high harmonics.