We demonstrate experimentally the quantum frequency down-conversion of a bright amplitude-squeezed optical field via a high efficiency difference frequency generation process. 532 nm amplitude-squeezed light with squeezing of 1.0 dB is successfully translated to 810 nm amplitude-squeezed light with squeezing of 0.8 dB. The effects of amplitude and phase fluctuations of the pump field on the frequency conversion are investigated both theoretically and experimentally. It is shown that the quantum frequency down-conversion is insensitive to small amplitude fluctuations of the pump field at the optimal conversion point. However, the phase fluctuations of the pump field can lead to increase of noise in the phase quadrature of the down-converted field. To eliminate the additive phase noise, a dual frequency down-converter which utilizing common pump field is proposed and demonstrated.