To analyze the influence of the chord length ratio and angle of attack on lift coefficients and explore the interaction mechanism between the two, we established a calculation model of the pressure distribution coefficient on the airfoil surface and lift coefficient of a dual-wing sail on the basis of the vortex panel method. Computational fluid dynamics was used in auxiliary calculation and analysis. Results revealed a reciprocal interference between the front-wing and rear-wing sails. The total lift coefficient of the dual-sail increased with an increase in the front sail chord length. The lift coefficient of the rear sail decreased with an increase in the front sail chord length or angle of attack. The front sail wake affected the pressure distribution on the upper and lower surfaces of the rear sail leading edge.