The structure of tapered fiber is of great significance to optimize the optical performance of tapered fiber amplifier. The variation of evanescent wave transmission depth of tapered fiber with different structure forms is analyzed, and two optimization schemes of tapered fiber structure are proposed. Combined with rate equation, power equation and finite difference beam transmission method, the model of quantum dot tapered fiber amplifier is established, and the influence of tapered fiber structure form on the performance of the amplifier is studied. The simulation results show that changing the initial melting length and stretching length can make the incident angle closer to the critical angle under the condition of total reflection, so as to increase the evanescent wave depth on the surface of the cone. The optimized tapered fiber structure is conducive to the improvement of the performance of the fiber amplifier.