The biased flow occurs when two side-by-side square cylinders are closely arranged. Wind tunnel tests are performed to investigate the aerodynamic characteristics of two side-by-side square cylinders in the biased flow regime. The Reynolds number Re is 8.0×104 and the spacing ratio T/B is in the range of 1.25~5， where T is the central spacing and B is the breath of a square cylinder. The variations of surface pressure coefficients， aerodynamic forces， and Strouhal number with spacing ratio are studied through the lateral wind tunnel tests. With respect to the biased flow regime， the temporal characteristics， spectral characteristics， and spanwise correlation of the aerodynamic forces are significantly discussed. The biased flow phenomenon mainly occurs in the range of T/B = 1.25~2， its direction is random and it disappears with the increase of spacing ratio. In the biased flow regime， the mean drag coefficients and fluctuating pressure coefficients of both cylinders are smaller than that of a single square cylinder， while the negative pressure on the gap-side surfaces of two cylinders is stronger than that on the side of a single square cylinder. Compared to the cylinder with a wider wake， the square cylinder with a narrower wake is characterized by stronger mean drag， fluctuating forces， gap-side negative pressure， and spanwise correlation of aerodynamic forces.