The invention provides a foreign matter invading detecting method and a foreign matter invading detecting device. The foreign matter invading detecting method comprises the following steps that infrared images within the monitoring scope are acquired by utilizing an infrared camera and are transmitted to an image collecting and processing system; whether a suspected foreign matter appears in the monitoring scope or not is determined by the image collecting and processing system according to the infrared images; when the suspected foreign matter appears, the laser light source and a visible light camera are focused on the suspected foreign matter within the monitoring scope, and filling light of laser light is conducted on the suspected foreign matter by utilizing the laser light resource; visible light images of the suspected foreign matter are acquired and transmitted to the image collecting and processing system; image registration and image fusion are conducted on the visible light images and images of the suspected foreign matter area in the infrared images by the image collecting and processing system; and information of the suspected foreign matter is provided by utilizing the fused images, and feature extraction and classification are conducted on the suspected foreign matter by utilizing the information of the suspected foreign matter, automatic identification and alarming for the suspected foreign matter are realized, and abundant and complete image information can be acquired in the time of dark light, dark skies and low visibility.