The femtosecond pulsed laser and pump-probe method have been used to measure the transient change of reflectivity of YBa2Cu3Ｏ７－δ(δ=0.0, 0.1, 0.4 and 0.8) thin films. From the experimental curves the transient changes are found to be very different for samples with different oxygen content. The sign of the changes can be reversed as decreasing the oxygen content. It may be attributed to the changes of energy band structure near the Fermi level. After fitting the experimental data, we reveal that the electron-phonon coupling in the sample of δ=0.4 is much weaker than high Tc(δ=0.0) sample.