The power distribution of the tapered fiber has been investigated based on Maxwell’s equation and the Taylor series expansion method. Following rigorous analytical approach, the general expressions for power in the core are derived, and a study is presented for the power distribution along the propagation direction in respect of different lower order modes. It is observed that the variation of the taper length, taper ratio, and refractive index can influence the power distribution of different fiber modes dramatically. The leakage loss, the taper length, taper ratio should be decreased. And refractive index difference should be increased if the light is launched from the smaller core-size end. And the taper length, taper ratio and refractive index difference should be increased if the light is launched from the larger core-size end to confine the power efficiently. When the fiber has long length and large taper ratio, the influence of refractive index on the power distribution is small compared with those of taper length and taper ratio.