The transmission spectra of cascaded longperiod grating (LPG) are analyzed using transfer matrix method. The effects of the length,position and loss coefficient of the fiber that connects the LPGs on the cascaded LPG spectral characteristics are discussed. Through numerical analysis, it is shown that the spectra of cascaded LPG and phase shifted LPG have great consistency when the length of the cascading fiber is small or the cascading position is near the end of the cascaded LPG. If other losses are not considered, the amount of transmission loss keeps constant no matter how the length of the cascading fiber changes. The calculation and analysis results also show that if the loss coefficient of the cascading fiber's cladding mode is large enough, the spectra of cascaded LPG can be dealt as incoherent cascading of two LPG spectra, which provides an efficient way to the optimization and design of LPG gain equalizer.