The sensitive mechanism of the airflow tilt sensor was analyzed by finite element method. The streamfield caused by heat source, when the three-dimensional enclosure inclining, has been obtained by a series of procedure,such as model building, meshing, loads applying and equation solving. In the process, ANSYS-FLOTRAN CFD program is employed. In horizontal status, the velocity of gas flow is equal at the two thermistor wires; therefore the current of both wires are also equal and the output of the bridge circuit is zero. In tilting status, the velocity difference of gas flow at the two thermistor wires will change with the tilt angle; therefore lead to changing of the current difference of both wires, the bridge outputs avoltage signal corresponding to the tilt angle. This calculation method provides a new approach to optimization of airflow tilt sensors.