The present invention relates to a PI3K inhibitor, and a pharmaceutically acceptable salt, polycrystalline form, and application thereof. The invention specifically provides a polycrystalline form of 4-chloro-5-(6-(1-(methylsulfonyl)cyclopropyl)-2-morpholinopyrimidin-4-yl)pyridin-2-amine, a pharmaceutically acceptable salt thereof, or a polycrystalline form of the salt. The invention further discloses a pharmaceutical composition comprising the inhibitor and an application of the pharmaceutical composition.