An OLED display panel and a photomask are provided. The OLED display panel includes a plurality of pixel areas arranged in a matrix on a plane. Each of the pixel areas is defined by an electrode and an organic light emitting material. The pixel areas increase in size along a first direction and the pixel areas increase in size along a second direction perpendicular to the first direction. The application solves the problem of non-uniformity in displaying images, caused by a feed-through effect in existing arts.