The Qianzhousaurus sinensis was first discovered in the Jiangxi Province of China, offering a unique glimpse into the ancient ecosystems that flourished in the Late Cretaceous. Qianzhousaurus is classified within the Tyrannosauroidea infraorder, specifically belonging to the Tyrannosauridae family.

Qianzhousaurus, estimated to be of medium size within the tyrannosaurid group, measured approximately 6.3 meters (20.7 feet) in length, with a hip height of 2 meters (6.6 feet) and a body mass ranging between 750 and 757 kg (1,653 and 1,669 lb). Some higher estimations propose a potential maximum length ranging from 7.5 to 9 meters (25 to 30 feet). This taxon can be distinguished from other tyrannosaurids by its distinct characteristics, such as a notably narrow premaxilla, a pneumatic opening on the upper portion of the maxilla, and the absence of a vertical ridge-like structure on the lateral surface of the ilium.

In contrast to more conventional tyrannosaurids, known for their robust jaws and thick teeth, Qianzhousaurus featured an elongated snout with narrow teeth when reconstructed. Notably, the holotype specimen, which is larger and more mature compared to the holotypes of both Alioramus species, still exhibited some unfused sutures between the cervical and dorsal vertebrae, suggesting its status as an immature animal, likely a sub-adult. Qianzhousaurus displayed long legs, with a femur measuring 70 cm (28 inches) in length and a tibia measuring 76 cm (30 inches) in length.

The identification of Qianzhousaurus initiated the recognition of a novel branch within the tyrannosaur family. This group, termed the Alioramini tribe, initially raised questions about its position in relation to other members of the tyrannosaur lineage during the initial investigation.

While many predators employ ambush tactics, swiftly lunging from concealed spots to chase down prey, Qianzhousaurus, despite its superior speed compared to larger tyrannosaurs, might have encountered difficulty sustaining a pursuit against a medium-sized ornithomimid. This is where its elongated snout becomes significant - Qianzhousaurus wouldn't have needed to outpace its prey; it just had to approach it within striking distance of its jaws. In terms of ecological niche, Qianzhousaurus likely occupied an intermediate position between smaller predatory dinosaurs like dromaeosaurs and troodonts, and its larger tyrannosaur relatives.

Among other dinosaur species, Qianzhousaurus could have potentially interacted with oviraptorids such as Banji, Ganzhousaurus, Nankangia, Huanansaurus, and Jiangxisaurus. Additionally, encounters might have occurred with therizinosaurs like Nanshiungosaurus, as well as the sauropod Gannansaurus.