To　investigate　the　effect　of　silencing　SET　gene　on　the　biological　characteristics　of　acute　promyelocytic　leukemia　NB4-R1　cells.The　expression　vector　of　pGCSIL　containing　SET-shRNA　were　transfected　into　293T　cells　by　using　other　packaging　plasmids.　The　supernatant　of　the　293T　cells　was　harvested　for　lentivirus.　The　SET-shRNA　lentiviral　vector　was　transfected　into　acute　promyelocytic　leukemia　NB4-R1　cells　and　a　stably　transfected　cell　line　was　established.　Real-time　quantitative　PCR　and　Western　blot　were　used　to　assay　the　silencing　efficiency　on　SET　gene　and　the　expression　of　PP2A.　The　cell　cycle　distribution　was　tested　by　flow　cytometry.The　expression　of　SET　in　experimental　group　statistically　decreased　as　compared　with　that　of　the　control　group.　The　expression　of　PP2A　was　obviously　raised　at　the　level　of　mRNA　and　protein.　The　percentage　of　NB4-R1　cells　in　G0/G1　phase　significantly　increased,　while　the　percentage　of　cells　in　S　phase　significantly　decreased.The　silencing　gene　in　acute　promyelocytic　leukemia　NB4-R1　cells　using　SET-shRNA　lentiviral　vector　can　increase　the　expression　of　PP2A　and　interfere　of　the　cell　cycle　in　NB4-R1　cells.　This　study　has　laid　a　experimental　base　for　targed　therapy　of　patients　with　acute　promyelocytic　leukemia.