The thickness of a camera is proportional to the image distance, although the lens can be replaced by a flat optics, such as a meta lens. However, there is no suitable method to reduce this thickness for low-cost applications. Here we proposed a novel down-sampling slim camera based on a micro-lens array (MLA) and an array sensor. By down-sampling the multiple micro images with a suitable array sensor, an enlarged image directly appears. Since the imaging module only consists of a low-resolution array sensor and an MLA, the thickness of the camera can be reduced to sub-millimeter. The proposed low-cost slim camera is suitable for imaging and sensing of internet-of-things (IoT) in particular. It also has a great application potential in the imaging of non-visible light.