Abstract: Icewater mixture，07 mmol／L cycloheximide and 02 ％ colchicine were used as pretreated reagent for Liriodendron hybrids root tips of testtube plantlet by different time grads. Then the root tips were squashed with Carbol fuchsin and observed with microscope. It had been proved that all these three pretreatments of icewater mixture for 6 h， 07 mmol/L cycloheximide for 2 h， and 02 ％ colchicine for 4 h could obtain metaphase chromosome specimen， but by comparison， root tips pretreated with cycloheximide and colchicine could give much better chromosome morphology. Then Karyotype of the Liriodendron chinense×L.tulipifera was studied with chromosome samples prepared from root tip by 07 mmol/L cycloheximide for 2 h. The result showed that there were 38 chromosome in Liriodendron chinense×L.tulipifera and its karyotype formula was 2n=38=26m+8sm+2st+2t and the karyotypes of Liriodendron chinense×L.tulipifera belong to category 2B of Stebbins.