The present disclosure provides a non-volatile flash memory device and a manufacturing method thereof. The non-volatile flash memory device comprises at least a plurality of memory cells in a memory area. The manufacturing method comprises: providing a substrate, and defining the memory area of the non-volatile flash memory device on the substrate; forming a plurality of stack gates of the plurality of memory cells on a substrate corresponding to the memory area, and the top of each stack gate is a memory control gate of the memory cell; etching the memory control gates to reduce the height of the memory control gates with the fluid photoresist filled among the plurality of stack gates of the plurality of memory cells as a mask; and removing the fluid photoresist.