White organic electroluminescence devices (OLEDs) were fabricated, with BCzVB as blue luminescence dye and Btp2Ir(acac) as red phosphorescence dye doped into CBP substrate as the light-emitting layer. The reason for the system color-coordinate shift is explored. For the device with the doping mass fraction of 6% BCzVB and 0.2% Btp2Ir(acac), the color-coordinate shifts slightly from (0.340, 0.273)to(0.308, 0.273), when the driving current varies from 4 to 200 mA/cm2. The reason of the slight blue shift is derived by the luminescence spectrum and luminance-current density curve. It is found that internal physical processes, such as the complete energy transfer from host CBP to dopant Btp2Ir(acac) and incomplete energy transfer from blue dye of BCzVB to red dye of Btp2Ir(acac), and luminesence saturation of phosphorescent dye of Btp2Ir(acac) determine the slight blue shift.