On the one hand, the thrust reverser that operate on ground only will prevent accidental opening in air in order to comply with the CCAR 25.933; on the other hand, it is required to deploy reliably and rapidly when landing on the ground. Therefore, judging whether the aircraft is on the “ground or in the air” has become very important for the control design of thrust reverser. If the “ground/air” definition that judge the aircraft is on ground is too rigid, the thrust reverser can not be opened as soon as possible when landing, affecting the efficient role of the thrust reverser at high speed on the contrary, if the definition is too loose, it will increase the probability of accidental opening of the thrust reverser in the air. This paper analyzes the “ground/air” definition of thrust reverser for several civil aircraft in service, and considers that the main land wheels just touch the ground (but does not necessarily trigger the wheel load signal) is a good time to deploy. In the design, it should be noted that the definition to deploy should be independence: any two of the thrust reverser, wheel braking or spoiler speed braking can not work at the same time due to the failure of a judgment signal. The thrust reverser cannot be opened due to the working state of the wheel braking or spoiler speed braking. At the same time, it shall be noted that the definition have influence on the means compliance with CCAR requirements.