Red phosphorescent microcavity organic light-emitting device( MOLED) with structure of Glass / DBR / ITO / Mo O3( 1 nm) /Tc Ta( 55 nm) /CBP∶ Ir( piq)2acac( 44 nm,6%) / TPBI( 55 nm) /Li F( 1 nm) / Al( 80 nm) was fabricated. For comparison,an OLED without cavity also was fabricated. The effect of microcavity structure on luminescent properties of phosphorescent devices was studied. The electroluminescence( EL) spectrum peak of OLED is at 626 nm,and the full width at half maximum( FWHM) is 92 nm. The electroluminescence( EL) spectrum peak of MOLED is at628 nm,and the FWHM is 42 nm which is narrowed half compared with the 92 nm value. The micro cavity structure can narrow the luminescence spectrum of OLED and improve the colour purity.For MOLED,the maximum brightness,the maximum current efficiency,the maximum external quantum efficiency( EQE) are 121 000 cd / m2,27. 8 cd /A and 28. 4%,respectively. For OLED,its maximum brightness,current efficiency and external quantum efficiency are 54 500 cd / m2,13. 1cd / A and 16. 6%,respectively. Comparing with the no cavity device,the luminescence properties of microcavity device have been improved greatly.