Rotary variable differential transformer （RVDT） adopts non-contract design， has the advantages of high sensitivity， good linearity and compact structure， and is widely used in automatic control system in the aviation field. The air gap between stator and rotor is one of the important structural parameters to improve its performance and reliability. This paper studies the air gap between stator and rotor and develops an optimized design with a typical product. Through theoretical simulation analysis and physical experimental tests， the influence of the air gap on the linearity and gradient of RVDT， the two important static indicators， is studied. In this way， under a certain structure size， the influence of the air gap size on the RVDT output gradient and linearity and the reasonable selection range of the air gap are obtained. The proposed study can not only provide strong support for the selection of product structure design parameters， but also revise the actual product structure size during engineering realization to improve the product qualification rate. In addition， the relevant research methods and conclusions obtained can also be promoted and applied to the development of redundant RVDT， providing a reference for the rapid development of such products.