A flash spinning method for preparing non-woven fabrics based on microwave thermal fusion, a microwave thermal fusion device, and a non-woven fabric preparation device are provided. The flash spinning method includes: step S1, collecting filament bundles to form a non-woven fabric precursor, adding a microwave heating liquid to the non-woven fabric precursor; the microwave heating liquid being configured to absorb microwave energy and convert the microwave energy into thermal energy; and step S2, performing microwave heating on the non-woven fabric precursor containing the microwave heating liquid obtained in the step S1 to obtain a heated non-woven fabric, and performing a hot press forming treatment on the heated non-woven fabric to obtain a finished non-woven fabric. There is no temperature gradient in layers of the non-woven fabric precursor, thereby significantly improving the peeling strength of the finished non-woven fabric.