The invention discloses a device for generating ultrahigh pressure. The device is capable of carrying out X light diffraction experiment, especially neutron diffraction experiment, is capable of integrating multiple measurement means, such as electrical transportation and spectra. The device comprises a primary pressure cavity, a secondary pressure cavity formed by eight secondary anvils, a sealing pad capable of penetrating through X light or neutron, a high-temperature and high-pressure assembly capable of being put into a space formed by the end surfaces of the anvils and the sealing pad, and a steel ring for supporting the eight secondary anvils, wherein the primary pressure cavity is driven by a belt-type press and formed by upper and lower tungsten carbide anvils; the steel ring is provided with an incident window and an emergent window. The device integrates the advantages of an opposite-anvil small press and a slide block-type multi-anvil large press, has the advantages that the opposite-anvil press is small and flexible and the multi-anvil large press is capable of providing enough lateral support and a relatively large sample size, and is very suitable for integration of in-situ X light/neutron diffraction experiment and measurement means, such as electrical transportation and spectra. The device has the advantages that the generated pressure is high, a large-size sample cavity is formed and multiple in-situ tests can be carried out.