In this paper the amplification equation of solitons propagating in Er3+-doped optical fibers is established by using the semi-classical theory. This equation takes into account of pump excited-state absoption so that it is applicable to the pump wavelength regime of 0.5-1.49μm. This equation is also applicable to the optical fibers with abitrary refrective index profile. abitrary pump and signal optical wave modes, abitrary doping contribution，homogeneous and inhomogeneous broadening and lumped and distributed amplification, which is a necessary elementary analytical equation for a profound research of tiie characteristics of soliton amplification in the Er3+-doped optical fibers and optirnizing its design.