The invention relates to a fixed-length cutting device for cotton packaging polyester strapping tape. The device comprises an induction type automatic tensioning buffering area support and an area-partitioned automatic speed regulating fixed-length cutting machine. A frame support is arranged in the induction type automatic tensioning buffering area support. Fixed rollers are arranged on the frame support. Sliding assemblies are arranged on the frame support and provided with the fixed rollers. Proximity sensors are arranged on the frame support. Tape conveying mechanisms are arranged in the area-partitioned automatic speed regulating fixed-length cutting machine and provided with cutting mechanisms. Guiding mechanisms are arranged behind the tape conveying mechanisms. The fixed-length cutting device has the beneficial effects of being convenient to use, capable of guaranteeing the yield and the quality of the product and stable in using performance.