The utility model belongs to a series of profile products for UPVC doors and windows, in particular to a multi-chamber UPVC profile casement window. The purpose is to improve thermal insulation performance. The casement window includes an insulating glass and a frame structure around the glass. The frame structure includes a casement frame profile and an inner-opening fan profile that are connected in a lap joint manner. The fan profile and the double-layer glass bead profile are connected with the insulating glass through the glass sealing strip; the glass backing plate profile is fixed by snapping into the groove installation structure of the casement profile through the tenon structure on it; the casement profile and the inner The open fan profile has a multi-chamber thermal insulation structure. The multi-layer chamber design of the window profile section can effectively improve the thermal insulation capacity of the profile itself, and the large size section also improves the structural strength. The standard European-style hardware installation interface is adopted, which is fully compatible with the high-end casement, flat-opening, etc. commonly used in the market. The inner opening and upper hanging hardware kit has strong practicability and market prospect.