Sail-assisted navigation is one of the effective ways to reduce carbon dioxide emissions in ship industry. In this study, a sail array consisting of six hard sails with a cross section of NACA0018 airfoil was designed. The lift and resistance of each sail were analyzed by numerical simulation under three conditions: upwind, crosswind and downwind. By comparing with the single sail case, the law of inter-sail interference on sail propulsion performance was explored. The confidence level of several independent geometric parameters on the propulsion performance of the sail array was evaluated by combining the experimental design method with ANOVA. The results show that the significance level of the independent parameters is highly dependent on the apparent wind direction. By changing sail layout and using non-uniform angle of attack, the propulsion performance can be better than that of single attack angle. This study is helpful to find the main parameters affecting the thrust performance of a multi-sail propulsion system and support for its global manipulation.