The invention relates to a preparation method of 2-phenylamino-6-dibutylamino-3-methylfluorane, which comprises reacting 2-methyl-4-methoxy diphenylamine and 4-dibutylamino keto acid in 93-98% sulfate, controlling reaction temperature at 10-20DEG C and keeping the temperature for 2-20h, pouring the reaction solution into ice water to be solidified, filtering to obtain condensate, adding 30% sodium hydroxide, processing neutralization and cyclization in the presence of strong alkali while pH value is higher than 10, refluxing at 90-100DEG C, reducing temperature of 20DEG C, crystallizing and filtering to obtain 2-phenylamino-6-dibutylamino-3-methylfluorane. The invention can reduce the generation of side product and carbonizing matter in reaction, reduce reaction time, reduce cost and reduce the discharge of waste water in process.