Standing on the potential for high-speed modulation and switching in the terahertz (THz) regime,all-optical approaches whose response speeds mainly depend on the lifetime of nonequilibrium free carriers have attracted a tremendous attention.Here,we establish a novel bi-direction THz modulation experiment controlled by femtosecond laser for new functional devices.Specifically,time-resolved transmission measurements are conducted on a series of thin layers Bi2Se3 films fabricated straightforwardly on Al203 substrates,with the pump fluence range from 25 μJ/cm2 to 200 μJ/cm2 per pulse.After photoexcitation,an ultrafast switching of THz wave with a full recovery time of～10ps is observed.For a longer timescale,a photoinduced increase in the transmitted THz amplitude is found in the 8 and 10 quintuple layers (QL) Bi2Se3,which shows a thickness-dependent topological phase transition.Additionally,the broadband modulation effect of the 8 QL Bi2Se3 film is presented at the time delays of 2.2ps and 12.5ps which have a maximum modulation depth of 6.4％ and 1.3％ under the pump fluence of 200 μJ/cm2,respectively.Furthermore,the absorption of α optical phonon at 1.9 THz shows a time-dependent evolution which is consistent with the cooling of lattice temperature.