The utility model discloses a demoulding mechanism of periphery inward back-off type, which comprises an upper fixing plate, a cavity fixing plate, a cavity, a core, a core fixing plate, an upper ejector retainer plate, a lower ejector retainer plate, a support post, a lower fixing plate, an ejector block, an ejector block connecting rod, an ejector pin of an injection molding machine, an auxiliary ejector retainer plate which is connected with the ejector pin of the injection molding machine, a secondary ejector mechanism which is mainly arranged between the auxiliary ejector retainer plate and the lower ejector retainer plate, and product separating mechanisms which are arranged between the upper ejector retainer plate and the ejector block, and between the lower ejector retainer plate and the ejector block. The demoulding mechanism of periphery inward back-off type pushes the upper ejector retainer plate and the lower ejector retainer plate to move upwards through the secondary ejector mechanism, and then separates products from the ejector block through the product separating mechanism; the demoulding mechanism of periphery inward back-off type can separate the products from the ejector block automatically, thus realizing automatic production of moulds, saving labor cost, and increasing production efficiency and yield of the products.