In-Flight Thrust Determination (IFTD) test subjects play a crucial role in the domain of civil aircraft. They are vital for precisely determining engine performance parameters. This includes accurately calculating the relationship between the engine’s N1K parameter and thrust as well as the fuel consumption rate. Moreover, they are indispensable for calibrating engine performance charts. In this paper, a comprehensive study is conducted. Based on a specific model, the thrust equilibrium state corresponding to various N1K values during steady-level flight is analyzed. This analysis not only focuses on the equilibrium state but also quantitatively presents the detailed aircraft configuration requirements under different N1K conditions. Through verification with actual flight test results, it has been demonstrated that this proposed method holds significant value. It can effectively direct the implementation process of IFTD flight tests. Additionally, it contributes to enhancing the efficiency of the entire flight testing procedure, which is of great importance for the development and optimization of civil aircraft engine performance evaluation.