The invention discloses a detecting and blanking mechanism for a steel ball sorting system. The detecting and blanking mechanism for the steel ball sorting system is characterized by comprising a test platform, wherein the test platform comprises a platform plate which is obliquely arranged along a length direction of the test platform; side plates are arranged on two sides of the width direction of the platform plate; a higher end of each side plate is located under a discharging opening of a feeding device; the other end of each side plate is arranged above a higher end of a sorting rolling channel, and is provided with an enclosure plate which can be opened and closed; a plurality of circular holes are formed in the platform plate; a steel ball seat with a ball-socket-shaped upper surface is arranged at each circular hole in a matching way; the edge diameter of ball sockets of the steel ball seats is smaller than the diameter of steel balls to be detected; a through hole is formed in the bottom of each steel base seat; blanking mechanisms capable of passing through the through holes and pushing-falling the steel balls to fall are arranged under the platform plate. The detecting and blanking mechanism of the steel ball sorting system has the advantages that the steel balls can be rapidly fed, the detection of a machine vision system is facilitated, qualified steel balls and unqualified steel balls can be pushed into the sorting rolling channel without mutual interference, and the steel balls can be accurately sorted.