The present invention provides a support assembly mounted between a rear cover and a screen of a handheld electronic device to support and fasten a component of the handheld electronic device. The support assembly includes an appearance part and an internal structure support part, where the appearance part and the internal structure support part are fabricated through integral molding of an amorphous alloy; the internal structure support part is formed by extending the top or the middle of the appearance part inwards; and an average thickness of the internal structure support part is less than 2 mm. The present invention simplifies a process of assembling the handheld electronic device. The present invention further provides a support assembly fabricating method and a handheld electronic device.