To meet the need of multi-channel optical spectrum analysis of weak l ight signals in spectroscopic studies,a design scheme of 32-channel fiber array and lock-in amplifier based optical spectrum analyzer is presented.32-channel fiber array is used for transmitting the linear light si gnals,and the detected signals converted by photodetectors are processed by a 32-channel synchronous digital lock-in amplifier.The field programmable gate array (FPGA) based 32-channel synchronous digital lock-in am plifier is designed to realize the function of detection for weak light signals simultaneously.Considering the strong interference whose frequency is 1kHz in measurement of femtosecond laser spectroscopy,a notch fil ter with the center frequency of 1kHz is designed to improve the dynamic range of signal measurement.The designe d spectrum analyzer has a spectral range from 400nm to 1100nm and a spectrum interval of 4nm.Experimental results show that the 32-channel fiber array input optical spectrum analyzer can run with a channel isolation up to 80dB,input light noise of 37.9fW/Hz,sensitivity limitation as low as 18.9fW and dynamic reserve up to 120dB.The designed optical spectrum analyzer is applied for the measurement of femtosecond time resolved f luorescence spectroscopy,and the strong ability of suppression for super fluorescence is presented.Meanwhile,t he sensitivity is improved and the measurement time is reduced to 6min.The designed optical spectrum analyze r can achieve multi-channel synchronous detection and spectrum analysis of weak light signals,with the adva ntages of high sensitivity,small size and low cost.