This paper solves the newly constructed nonlinear master equation dp/dt =κ[2f(N)αρ(1/f(N-1))α(+)-α(+)ρ-ρα(+)α],where f(N)is an operator-valued function of N = α(+)α,for describing amplitude damping channel,and derives the infinite operator sum representation of quasi-Krans operators for the density operator.It also shows that in this nonlinear process the initial pure number state density operator will evolve into the binomial field(a mixed state)when f(N)= 1/√N+1.