Abstract: The effect of irregular-void on transverse tensile properties of unidirectional fiber-reinforced composites was studied. Firstly, irregular-void random algorithms were programmed by C⁺⁺. Secondly, the repeating unit cell (RUC) of the composites microstructure with random fibers and irregular-void was generated by Python. Then, the effect of irregular-void on transverse modulus and transverse tensile strength of unidirectional composites was simulated by the finite element method (FEM). It is found that void shape affects the initial damage, damage evolution and final damage of RUC. As void content increases, both transverse modulus and transverse tensile strength decrease. The effect of void content on transverse tensile strength is larger than on transverse modulus.