Provided is a phosphorus-modified MFI-structured molecular sieve. The value of K of the molecular sieve satisfies that 70%≤K≤90%, for example, 75%≤K≤90%, furthermore, for example, 78%≤K≤85%, wherein K=P1/P2×100%, P1 represents the mass content of phosphorus within an area of 100 square nanometers and a vertical depth of 0-2 nm of any crystal plane of molecular sieve crystal grains measured by an XPS method, and P2 represents the mass content of phosphorus within an area of 100 square nanometers and a thickness interval of 5-10 nm of the vertical depth of any crystal plane of the molecular sieve crystal grains measured by an EMPA method. Also provided are a cracking auxiliary agent or a cracking catalyst containing the phosphorus-modified MFI-structured molecular sieve, as well as a preparation method therefor and an application thereof.
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