The time evolution of electron temperature in plasma current rising phase on CT-6B Tokamak is estimated by the history method for oxygen impurity lines. The time variations of line emissions of OII-OV1 in VUV region are measured by one-meter grazing incidence vacuum spectrometer and the electron density is measured by using FIR HCN laser interferometer. The switch-on time of each line emission is used for estimating electron temperature. The influences of oxygen impurity influx rate and confinement time on intensity and switch-on time of line emissions are surveyed numerically. The estimated electron temperatures arc around 3.6, 5.6, 7.3, 10.8 and 21 eV, respectively at 0.36, 0.56, 0.66, 0.90 and 1.4 ms after the start of discharge, which indicate the plasma temperature in central region.