Abstract: The in-plane shear properties for the unbalanced 2.5D carbon fibre woven preforms (2.5D CFWPs) due to the changing of yarn linear density were investigated by the bias-tensile test. The test materials including 4 kinds of unbalanced 2.5D CFWPs and 1 kind of balanced 2.5D CFWPs. The typical bias-tensile modes and meso-structures were observed; The shear angles and bias-tensile load of balanced and unbalanced samples were compared and analyzed; Normalized method was used to analyze the influence of yarn linear density on the in-plane shear properties. The results show that the typical bias-tensile modes of the unbalanced 2.5D CFWPs are asymmetric S-shape or Z-shape. The bias-tensile properties of unbalanced 2.5D CFWP samples with yarn linear density of 792 tex×396 tex(the warp is 792 tex and the weft is 396 tex) are similar, the other 2 unbalanced samples are similar too; The bias-tensile load of the balanced samples is larger than the unbalanced, After locking angle, the bias-tensile load of the balanced samples is rising rapidly and the unbalanced is rising slowly; The normalized shear forces of the all 5 kinds of 2.5D CFWP samples are similar when the shear angle is less than 20.81°, and the 4 kinds of unbalanced samples are similar when the shear angle is between 20.81°-30.02°.