Firstly, the principles of fiber-optic parametric amplifier with cascaded structure were introduced. Then, the signal output gain expression about the single-pumped and cascaded fiber optic parametric amplifier was derived at small signal approximation. The gain characteristics were analyzed by using Matlab software. The results show that the peak gain and gain bandwidth of the cascaded fiber parametric amplifier are affected by the number of segments, pump power, pump wavelength, DCF length and high nonlinear fiber (HNLF) zero-dispersion wavelength, HNLF length, HNLF nonlinear coefficient and HNLF dispersion slope.