Abstract: Laser ceilometer is one of the most powerful instruments to monitor the spatial and temporal distribution of cloud automatically and uninterruptedly. For the reason of algorithm, low signal-to-noise ratio and existence of aerosol layer may lead to inaccuracy during cloud observation. Based on the analyses to raw signal, differential signal and second-order differential signal, the differential enhancing method for detection of cloud was presented as well as the construction of two new signal series. The new method could realize the enhancement and separation of the signal feature of cloud peak and boundary and results in reduction of influence of low signal-to-noise ratio and existence of aerosol layer. Comparison experiments using both the differential zero-crossing method and the differential enhancing method were conducted. The results show the differential enhancing method can reduce the rates of missing judgement and misjudgement while has no influence to the judgement of cloud heights.