Blended wing body (BWB) configuration will be the inevitable trend of the aircraft using in the future civil aviation for its excellent performance. Aerodynamic and flow mechanism investigations of the BWB configuration will provide important support for its design. Wind tunnel tests include force measurements and tuft visualization, in addition to computation fluid dynamics (CFD) simulation，are used to investigate the low speed aerodynamic characteristics and flow mechanism and effects of flow-through nacelles for a 300-passenger BWB configuration(BWB-1). Test results show that longitudinal aerodynamic characteristics of BWB-1 are better than those of the Early BWB or N2A. BWB-1 possesses lateral static stability and directional static instability, however, low value of the directional instability degrades the difficulty in directional stability augmentation and control. Investigation also reveals flow development and physical mechanism of a mild stall characteristic of the configuration. Flow-through nacelles are beneficial to both maximum lift and directional stability, and have minimal effects on lateral stability; however, drag and pitch-down moment are increased. Results from CFD simulation show good agreement with tunnel data，which demonstrate the validation of the CFD method. The research results will provide useful reference for the development of next generation civil transport in China.