Drop sensor be used to detect liquid drops in IV set chamber, can used together with an infusion pump to control drop rate. Drop sensor should work normal even in condition of chamber deviation or directly exposed to environment light. Infrared components must careful select, light transmit and receive must calculate to get circuit parameter. Controlled by digital mode, align light strength, control width of light, simultaneously data sample, use pulses detect algorism. Finally, at the drop angle is within±45°,It can be used when the infusion pipeline is Lightproof or water miston the inner surface or different batches of photosensitive devices. So as to achieve accurate, low-power droplet detection.