The invention relates to a mesoporous P-IM-5 molecular sieve, wherein the diameter of the most probable mesopore is 3-15 nm, and the phosphorus content is 0.5-3.0% by mass (calculated as P2O5). According to the present invention, the molecular sieve can be directly prepared with the synthetic raw materials, can further be prepared by using the microporous IM-5 molecular sieve as the raw material through the secondary crystallization method, is used for the methylation reaction of toluene and methanol, and has advantages of high toluene conversion rate, high xylene yield and high activity stability.