This present invention discloses a manufacturing method and structure for a wafer level image sensor module with fixed focal length. The method includes the following steps. First, a silicon wafer comprising several image sensor chips having a photosensitive area and a lens module array wafer comprising several wafer level lens modules with fixed focal length are provided. Next, the image sensor chips and the wafer level lens modules are sorted in grades according to the different quality grades. According to the sorting results, each of the wafer level lens modules is assigned to be situated above the image sensor chip that has the same grade. At the same time, each of the wafer level lens modules is directed to face the photosensitive area of each image sensor chip. Finally, in the packaging process, the wafer level lens module is surrounded by an encapsulation material.