The invention provides a device and method for generating an 
extreme ultraviolet tunable monochromatic coherent 
light source, the method is characterized by utilizing interacting actions of 800 nm 
femtosecond laser and gas to generate ultraharmonics, tuning high order 
harmonic energy from the 
frequency comb to a specific degree through the macroscopic 
phase matching and atoms 
phase matching technology, and enabling the high order 
harmonic energy to output single high order 
harmonic (
monochrome) in a specific degree. Furthermore, the specific high order harmonic can conduct tuning through the phase-matching technique, that is, the output wave length is adjustable. The 
extreme ultraviolet tunable monochromatic coherent 
light source generated by the device can be used in the fields of high precision detection for micro-nano structures, high precision 
holographic imaging and high precision 
carving and the like, and can also be used as an injecting source of a 
free electron laser, and the application range is extremely broad. And the device has the advantages that 
extreme ultraviolet can be output, 
monochrome tuning is realized and the coherence is good.