The　effects　of　the　inertia　parameters　of　moving　platform　on　the　dynamic　response,　dynamic　stress　and　natural　frequency　of　flexible　parallel　mechanisms　were　studied.　The　mechanism　total　mass　function　is　combined　with　elastic　deformation　energy　function　by　using　linear　weighted　method　to　derive　the　multiple　objective　function,　and　the　boundary　condition　of　inertia　parameters,　motion　errors,　natural　frequency,　dynamic　stress　and　driving　moment　are　considered　as　constraint　equations　to　perform　the　optimal　design.　The　optimal　inertia　parameters　of　moving　platform　are　determined　based　on　the　optimal　design.　The　effects　of　the　inertia　parameters　are　well　illustrated　through　the　numerical　simulation　of　a　planar　3-RRR　parallel　mechanism.　The　inertia　parameters　of　moving　platform　are　demonstrated　to　have　significant　impact　on　the　dynamic　response,　dynamic　stress　and　natural　frequency　of　flexible　parallel　mechanism,　and　they　should　be　important　parameters　for　the　analysis　and　design　of　flexible　parallel　mechanism.