The deformation of the cladding tube triggered by the expansion of the internal plug is used to investigate the hoop deformation behaviour of the Cr-coated zirconium alloy cladding tube at room temperature. A thin-walled pressurized cylinder model is used to transform the axial load-displacement curve working on the expansion plug into the hoop stress-strain curve working on the cladding tube, and it is found that the Cr coating can be able to restrain the cladding tube from hoop deformation. Observation of the Cr-coated cladding tube after different amounts of hoop deformation revealed that the strain corresponding to the generation of the first crack was a ranged from 0.48 % to 0.59 %, the density of cracks started to grow very fast and then entered a saturation stage. The fracture strength of the Cr coating and maximum interfacial shear strength when the Cr coating crack density reaches saturation were calculated by the shear-lag model. Twins and a large number of dislocations were generated in the Zr matrix and a small number of dislocations in the Cr coating after the hoop deformation. The behaviour of crack initiation and propagation occurring in Cr coating is revealed.