The invention belongs to the technical field of medicinal chemistry, and specifically relates to an S isomer of N-(4-(3-fluorobenzyloxyl)-3-chlorophenyl)-(5-((2-(methylsulfinyl)ethylamino)methyl-2-furyl)-quinazoline-4-amine, ditoluene sulfonate (formula II) of the S isomer, and polymorphic substance of ditoluene sulfonate, and discloses a preparation method thereof. The data of biological tests shows that the provided S isomer and ditoluene sulfonate thereof can well inhibit the activity of EGFR and Her2 tyrosine kinase; and can also well inhibit the NCI-N87 tumor inhibiting model that highly expresses HER-2 in human body. The crystal form (A) of the compound represented by the formula (II) has a better solubility and better effect in human body.