Based on the properties of transient feeble optical signal,which is the wide dynamic range and the feeble lower limit signal,a novel detecting scheme compressing signal in logarithmic field is presented.After the principle analysis of the scheme,it is implemented to choose appreciate parts,design the circuitry and test.The results indicat that the approach can make transient optical signal ranged 120 dB compress in the range of 0~5 V.And together with the circuitry design simplifies and the dissipation decreases,the troubles at the back data acquisition module can be lessened greatly.