The invention relates to a counting method on the basis of a sleep timer. The method comprises the steps of firstly arranging a photosensitive element on a Murphy dropper side of a transfusion device, wherein the photosensitive element is used for inducting the changes of light intensity projected on the photosensitive element by penetrating through the Murphy dropper when a liquid drop drips; monitoring the dripping state of transfusion liquid drops; converting induction light intensity change pulse signals into electric pulse signals by virtue of a sensor constructed by the photosensitive element, and transporting to an I/O pin of a single-chip. The single-chip is used for counting the electric pulse signals by using the sleep timer with input capture functions, thus obtaining the dripping speed of transfusion. Compared with the prior art, because the counting method disclosed by the invention adopts ambient light as a signal input source, and the single-chip operation is in a sleeping mode, an adopted sleep counter interrupt counting mode has the advantages of low energy consumption, low load, accurate counting and the like.