An encapsulation assembly and a forming method thereof, and a vehicle window are provided. The method includes: forming a trim (100, 300) which includes a decoration section (120, 320) and a connection section (110, 310) with a penetration structure (111, 311) formed therein; and forming a gasket (200) which includes a fixing section (210) covering the connection section (110, 310) of the trim (100, 300), wherein a part of the fixing section (210) is filled into the penetration structure (111) of the connection section (110, 310). The encapsulation assembly includes: a trim (100, 300) which includes a decoration section and a connection section (110, 310) with a penetration structure (111, 311) formed therein; and a gasket (200) which includes a fixing section (210) coving the connection section (110, 310) of the trim (100, 300), wherein a part of the fixing section (210) is filled into the penetration structure (111, 311) of the connection section (110, 310). The vehicle window includes a piece of glass and the above encapsulation assembly. A part of the fixing section (210) of the gasket (200) can be filled into the penetration structure (111, 311). When the fixing section (210) of the gasket (200) covers the connection section (110, 310) of the trim (100, 300), the fixing section (210) can be fixed with the connection section (110, 310) of the trim (100, 300) through the penetration structure (111, 311), such that a more stable connection between the fixing section (210) and the trim (100, 300) can be achieved, which may increase the service life of the encapsulation assembly.