An optical liquid drop sensor(OLDS) which can be used to distinguish different liquids is presented in this paper. The main block ofthis system are a light path and a drop-forming head sensor. We can gain three kinds ofiniormation about the liquid to be measured with this OLDS system. That is optical signal representing light intensity information, electrical signal revealing volume information ofthe liquid drop and spectral signal displaying ingredient information of the liquid individually. Colligate this three kinds of information and after data-processing the fingerprint of the measured liquid can be derived. Due to different characteristics of various liquids, the fingerprint of one liquid differs from that of others. This difference has been proved through experiment. Thus the OLDS is valuable for the discrimination of different liquids and the measurement ofthe liquid's parameters.