The photoelectric liquid drop sensor(PLDS) is based on the optical fibers positioned inside the drop and the special capacitive sensor composed of the drop head and a cylindrical ring plate.LED,and a part of the processing circuit are integrated into PLDS,and the drop head together with several relative components are specially designed in mechanism.Therefore,some problems can be solved effectively,such as the serious loss of light intensity in transmission,the interference on the weak output signal,the instability of positions of fibers,the instability of drop profile caused by bubbles and difficulty in cleaning the drop head.Multi-wavelength optical signals are led into the drop through two source fibers.CCD image drop analysis can be easily carried out through the removable ring plate.