This reaction vessel adopts a flange straight through sight glass. During the reaction process, the shape and characteristics of the material constantly change. The observation effect and judgment of the sight glass are directly related to the product quality. It is urgent to have a reaction vessel sight glass with clear observation line and easy cleaning to meet the needs of observing the reaction process. The photochemical mirror reaction vessel, also known as the external illuminated photocatalytic reactor, can be used in industrial production such as chemical, petroleum, and pharmaceutical industries. The light window material is polished JGS2 quartz glass (pressure resistant window) or sapphire mirror, which can observe the flow and reaction of liquid, gas, steam and other media at any time to ensure normal experiments. It is also an important component of the reaction vessel. A reactor designed for photochemical catalysis, synthesis, degradation and other reactions, suitable for high-pressure photochemical reactions, carbon dioxide (CO2) reduction, carbon dioxide (CO2) reduction to methane (CH4), reduction degradation of nitrogen oxides (Nox), high-pressure photocatalytic degradation of formaldehyde and other fields. Suitable for reactions with a small number of samples, it is an ideal reaction device for testing expensive or low yield counterfeit raw materials.