Using optical pump-terahertz (THz) probe (OPTP) technology and changing the car rier concentration of the sample,we achieve the effective modulation of the THz transimition/reflect ion when changing the pump fluence.With the pump beam at 800nm,we achieve the effective modula tion on THz time domain spectroscopy.The modulation of THz time domain spectroscopy includes the modulation of the ampiltude and phase of THz wave,and the modulation of secondary reflection peak of THz wave by changing the pump fluence.With varying the pump fluence,more than 90% modulation of the ampiltude of THz wave can be achieved.Another phenomenon we observed is that a negative time shift of the terahertz pulse occurs when the silicon surface is photoexcited.Wi th pump fluence increases,and the frequency increases,negative phase shift is becoming more and more obvious.Varing the pump fluence,the secondary reflection peak shows a π phase shift or zero phase shift relative to that of i ncident pulse,and it acts as a broadband terahertz pulse antireflection coating with proper pump fluence.This modulation of THz time domain spectroscopy can lay the foundation for the applic ation of THz wave in communication, national defense and security fields.