A method for forming a mask pattern is provided, comprising forming a negative photoresist on a substrate; in an environment without oxygen, to performing a first exposure on the negative photoresist by use of a first ordinary mask plate, so that a fully-cured portion of the negative photoresist is exposed to light and a semi-cured portion and a removed portion of the negative photoresist are not exposed to light; in an environment with oxygen, performing a second exposure on the negative photoresist by use of a second ordinary mask plate, so that the semi-cured portion of the negative photoresist is exposed to light and the removed portion of the negative photoresist not exposed to light; removing the uncured negative photoresist and forming the mask pattern.