The invention provides a method for detecting printed circuit boards. The method comprises the steps of providing an interface to receive a to-be-detected area chosen on a printed-circuit-board scanning image generated through an optical detector by a user, recognizing a weld leg in the chosen area and detecting the weld leg. The invention also provides an optical detector for printed circuit boards. The invention solves the problems that the prior optical detector for printed circuit boards needs to manually draw test windows of IC weld legs one by one when the IC weld legs are detected or array the test windows of the weld legs through the quantity of the specified IC weld legs, and is complex to recognize and program the IC weld legs and high in detection workload, and then achieves the automatic recognition of a plurality of to-be-detected weld legs, as well as convenient fast effects. The method can greatly simplify the programming process for recognizing the IC weld legs in the use of AOI.