Abstract: Since tapered fiber works as a connector between multi-mode fiber and single-mode fiber to improve the coupling efficiency and transmits laser beam with high power and good beam quality under single-mode conditions, the power conversion efficiency of the tapered fiber is important. A method of melting and drawing tapered fiber was introduced and the transmi-ssion characteristic of tapered fiber was discussed. A Gaussian approximation model to calculate the conversion efficiency of tapered fiber was presented based on mode field coupling theory. The simulation result was discussed and an experiment was conducted with 532 nm laser, multi-mode fiber with NA=0.11, a=12.5 m and tapered fiber with NA=0.11, a=（41）m，(51)m(61)m，(71)m and (81)m respectively, to measure the conversion efficiency of tapered fiber. The experimental results agree with the theoretical prediction.