Abstract: Limited by equipment such as fire control radars near the nose, modern fighters cannot set pressure ports near the stagnation point, which causes the test accuracy of the conventional flush air data sensing system to greatly decline. For the diamond nose used in the typical fighter, the algorithm and accuracy of FADS (Flush Air Data Sensing) without stagnation pressure are studied. Through subsonic and transonic wind tunnel calibration experiments, the pressure distribution characteristics of the pressure ports were obtained and the FADS technology without stagnation pressure was constructed based on the Kalman filtering algorithm. The algorithm has been improved by importing differential pressure. The improved algorithm is partly decoupled, resulting in improved accuracy with few iterations and low computational complexity. The experimental results show that the algorithm without stagnation pressure can effectively work out air data in external experiment, with an accuracy of 0.33° for angle of attack, 0.30° for angle of sideslip, 0.67% for static pressure, and 0.011 for Mach number.