1. A photolithographic mask, comprising: a transparent substrate; an opaque layer formed on the transparent substrate; layout patterns with at least a first sub-resolution assistant feature and a second sub-resolution assistant feature with non-uniform size along the longitudinal direction formed in the opaque layer, wherein: the layout patterns include a dense patterns and isolated patterns; the dense patterns includes a plurality of first stripes arranged parallelly; the isolated pattern includes at least a second stripe and a third stripe arranged parallelly; and the first sub-resolution assistant feature and the second sub-resolution assistant feature are disposed between the second stripe and the third stripe.