Abstract: The present invention discloses an automatic cleaner for cleaning a surface. The automatic cleaner comprises: a light emitting device, configured to emit first light, wherein a first angle exists between a first emitting direction of the first light and the surface when the automatic cleaner is located on the surface, wherein the first angle is larger than 0° and smaller than 90°; an optical sensor, configured to detect first optical data generated based on the first light; and a processing circuit, configured to determine if the liquid or the colloid exists in a predetermined range of the automatic cleaner based on the first optical data. The processing circuit further determines a location of the automatic cleaner on the surface according to navigation optical data.