Abstract： Highly accurate performance prediction models based on the streamline curvature method for the through-flow analysis of transonic compressors was developed, of which the minimum loss incidence and off-design loss prediction model were modified. In addition, four-quadrant -analysis, an original method for off-design loss analysis, was proposed to redefine the composite of transonic compressor loss, to make a further exploration on the characteristic of loss at multiple operating conditions, and to reveal the loss distribution and growth law of transonic compressors to a certain extent. Detailed calculations of a highly loaded transonic compressor rotor with the newly developed model was conducted. The results show that the newly developed model and the four-quadrant-analysis method can reliably predict the overall performance and spanwise distribution of aerodynamic parameters at both design and offdesign operating conditions, providing a new idea for off-design performance prediction. In general, the newly developed model and analysis method can be of great service to engineering.