A method for forming composite is provided. The method comprises following steps. Firstly, a polypropylene homopolymer and at least one kind of inorganic particles are provided to a twin screw extruder, wherein the polypropylene homopolymer occupies 40 wt %˜90 wt % of the composite, the inorganic particles occupies 10 wt %˜60 wt % of the composite, the melt flow index of the polypropylene homopolymer is lower than 3.6 g/10 min, and the particle sizes of the inorganic particles are in a range of 100 nm to 1000 nm. The polypropylene homopolymer is heated to a molten state. Then, the molten-state polypropylene homopolymer and the inorganic particles are enabled to pass through at least five kneading blocks of the twin screw extruder to be mixed together such that the inorganic particles are dispersed in the polypropylene homopolymer.