The present application relates to metal cutting, and more particularly to a cutting fluid and a preparation method and an application thereof, especially the application in the processing of niobium-tungsten alloy (NB521). The preparation method of the cutting fluid is simple and requires low production cost. In the mechanical processing of niobium-tungsten alloy (NB521), the cutting fluid has good cooling performance, lubricity, load-bearing capacity, friction reduction and vibration absorption, and long service life. It also can effectively avoid built-up edges, thereby improving the service life of cutting tools and the processibility of materials. Therefore, products of good quality are produced to improve the yield, especially in the deep hole machining, and thus the cutting fluid of the present application is suitable for a wide range of applications.