The present disclosure provides a positive photoresist composition including a major adhesive material and a photosensitizer, wherein the photoresist composition further includes a photoisomerizable compound which would be converted into an ionic structure with an increased degree of molecular polarity after ultraviolet irradiation. The formation of the ionic structure with increased polarity of the molecule reduces the adhesion between the positive photoresist and the organic film layer, facilitates stripping after formation of the via, and improves the product rate of pass. Further, the present disclosure provides a via-forming method using the positive resist composition, a display substrate including the via formed by the via-forming method, and a display device including the display substrate.