A manufacturing method of a multi-level cell NOR flash memory includes the steps of forming a memory cell area and a peripheral circuit area with the same depth of a shallow trench isolation structure, and the depth ranges from 2400 Å to 2700 Å; forming a non-self-aligned gate structure; performing a self-alignment source manufacturing process; and forming a common source area and a plurality of drain areas. The manufacturing method achieves a high integration density between components and provides a better thermal budget and a better dosage control to the multi-level cell NOR flash memory to improve the production yield rate.