The transient carrier dynamics of CdSeS quantum dots is investigated by time-resolved femtosecond pump-probe transmission spectroscopy method at different photon energies and pump energy densities. The experimental results show that the relaxation of excited state of CdSeS quantum dots have three processes. The first one is a rapid relaxation process whose time scale is about 10 ps. The rapid process time constant increases when the pump energy density increases and is independent of the photon energy. We hold the opinion that the rapid process is caused by the carrier and the optical phonon scattering. The second relaxation process whose time constant is about 100 ps. The carrier relaxation time is independent of the pump energy density and photon energy. The component is associated with recombination via trap states. Then a slow decay process due to single exciton relaxation with a lifetime as long as nanoseconds can be observed. This process is attributed to inter-band relaxation. The transmission change increases with the increase of pump energy density at zero delay time. When the pump energy density increases to a certain extent, the transmission change under the zero delay gradually tend to be saturated.