In　atmospheric　environment,　the　additional　mass　produced　by　air　greatly　can　reduce　the　stiffness　of　a　planar　film　reflect-array　to　make　its　natural　vibration　characteristics　have　a　larger　error　compared　with　those　in　actual　vacuum　environment.　In　order　to　test　and　verify　dynamic　characteristics　of　a　planar　film　reflect-array,　considering　practical　tests　in　vacuum　environment　being　unmanageable　and　uneconomical,　an　equivalent　approach　to　measure　a　grid　film＇s　natural　vibration　characteristics　in　atmospheric　environment　neglecting　the　effect　of　additional　mass　produced　by　air　to　substitute　those　of　a　planar　film　reflect-array　in　vacuum　environment　was　proposed.　The　numerical　simulation　results　for　natural　vibration　characteristics　of　both　cases　were　contrastively　analyzed,　and　the　test　verification　was　conducted　using　biaxial　tension　device　and　non-contact　displacement　dynamic　collection　equipment.　Finally,　a　useful　formula　was　obtained　to　calculate　the　equivalent　natural　frequencies　of　a　planar　film　reflect-array　in　vacuum　environment　using　the　corresponding　test　values　of　a　grid　film　in　atmosphere　environment.　©　2019,　Editorial　Office　of　Journal　of　Vibration　and　Shock.　All　right　reserved.