The invention provides salt-resistant flushing liquid and a preparation method thereof. The flushing liquid comprises the following components in parts by weight: 100 parts of water, 0.5-1 part of a dispersing agent, 1-1.5 parts of a diluting agent and 3-8 parts of a regulating agent. The preparation method of the flushing liquid comprises the following steps: blending the dispersing agent, the diluting agent and the regulating agent with the water in proportion and uniformly stirring to obtain the salt-resistant flushing liquid. The salt-resistant flushing liquid provided by the invention is used in the salt water layer and large-section salt gypsum layer well cementation and has the advantages that the problems of too high system consistency, bad liquidity and high difficulty in ensuring the displacement efficiency occurring in the salt layer well-cementing process are solved with the cooperation of a salt-resistant cement slurry system, so as to improve the well-cementing quality and prolong the service life of an oil and gas well.