The invention discloses a metal hollowed-out structure prefabricated vacancy forming device and method, and relates to a forming device and a forming method. The problems that a traditional plastic forming method mainly uses a complete panel as the object, the weight reducing amplitude is limited, and the requirement for the light-weight structure cannot be met are solved. The metal hollowed-out structure prefabricated vacancy forming device comprises an upper pressing block, pressure springs, two guide columns, a male die, two edge pressing blocks and a female die. When the panel for preparing a hollowed-out plate is made of aluminum alloy or stainless steel, the method includes the steps of firstly, preparing the hollowed-out plate; secondly, placing the hollowed-out plate; and thirdly,exerting pressure. When the panel for preparing the hollowed-out plate is made of titanium alloy, magnesium alloy, high-temperature alloy or an intermetallic compound, the method includes the steps offirstly, preparing the hollowed-out plate; secondly, placing the hollowed-out plate; and thirdly, performing heating until the temperature Tm is reached and exerting pressure. The three-dimensional curved surface hollowed-out structure can be obtained.