Under the pumping of a 970nm diode laser the Tm3+ and Yb3+ codoped ZBLAN glass emits strong blue and red upconverted light.The luminescence of 1G4 and 3F4 levels results from the conse-quential Yb3+ to Tm3+ energy transfer,whereas the 1D2 level is excited by a further cross energy transfer among Tm3+ ions.The cross-relaxations of Tm3+ ions and back energy transfer of Tm3+ to Yb3+ was also observed.Furthermore,after an investigation of the special characteristic of Tm3+ and Yb3+ codoped system we think that this system is advantageous to the improvement of the net efficiency of upconversion luminesce.