Hollow built-in window blind

A hollow built-in blind comprising:

• an outer glass, an inner glass, a spacer, and a blind, said blind being installed in a closed space cooperatively defined by said outer glass, said inner glass and said spacer, said spacer having a cross section with a stepped portion to connect with said blind;
• said blind including a fixing device surrounded by said spacer, said fixing device including an upper rail having a cross section with a projection, and left and right frames each having a cross section with a projection, said spacer having an inner side proximate to said inner glass, an outer side proximate to said outer glass, and a four-sided interior surface in contact with said upper rail and said left and right frames, said interior surface being flat and free of any projection, said interior surface and said inner side being indented to cooperatively form said stepped portion at a junction of said interior surface and said inner side, said projections of said upper rail and said left and right frames of said blind being inserted between said stepped portion of said spacer and said inner glass, and being connected to said spacer;
• wherein said blind further includes
• a drive device including a plurality of cord-winding devices, a plurality of rope ladder turning mechanisms, a plurality of bearings and bearing seats to support said cord-winding devices, a tapered balance cord-reeling device wound with a balance pull cord, and a drive shaft to interconnect a blind actuating device, said cord-winding devices, and said tapered balance cord-reeling device;
• wherein each of said upper rail, said left frame, and said right frame has a U-shaped groove structure, and forms a rectangular cavity structure with a cover plate to receive said drive device and said blind actuating device;
• and
• wherein said cover plate is proximate to said inner glass and extends partially into said stepped portion and between said inner glass and each of said upper rail and said left and right frames.