In the production process of the injection, foreign particles are probably interfused into the injections, so the injections must be inspected before leaving the factory. An opt-electronic method is proposed based on light-blocking theory for foreign particles detected in injections, and the principle of this inspecting method is introduced. Compared with the conventional manual inspection method, the preliminary experimental results show that the new method has a satisfied conformance rate of 96.30% in the case of static offline detection. In order to improve the inspection effect, a method of dual-light-path is also proposed to avoid the foreign particles miss inspection in case of the track testing time is too short or the testing area is too small.