Abstract: Photosynthetic rate of apple trees may be improved and the phenomenon of“noon break” will be eased up to some extents after foliage top-dressing of potassium ．It will improve and extend the photosynthetic rate of the apple trees in the ssme year as well as increase the storage of nutrition after five times of spraying potasium in apple growth period form May to October，and the effects will be kept up for twenty-five days after every spraying of potasium．