The invention relates to a film patterning method, an array substrate and a manufacturing method of the array substrate. The film patterning method comprises steps that photoresist is coated on a to-be-patterned film; exposure and development of the photoresist are carried out, after exposure and development of the photoresist, an area corresponding to the completely-removed part is a first area; postbaking of the photoresist is carried out, high temperature melting down of the photoresist occurs to make the area corresponding to the completely-removed part change to be a second area, and the photoresist after postbaking form a mask pattern; the mask pattern is taken as a mask to carry out patterning of the film. The film patterning method is advantaged in that the high temperature melting down characteristic of the hot melt photoresist after development and postbaking is utilized, making the to-be-patterned film form a small-dimension pattern below exposure machine precision is possible, the process is simple, and cost is low.