In order to get ultra-short intensity laser pulses, it is necessary to amplify the laser pulses from nJ level to mJ level. The regenerativeamplifier is the best way to get high-energy laser pulse. It can amplify the seed from nJ level to mJ level quickly. And the output laser has a good spatial mode. A Ti:sapphire regenerative amplifier was designed in this paper.Otherwise, in order to make the output laser stable, a 1 kHz 527 nm green laser was used as the pump laser in the experiment. Using such a Ti:sapphire regenerative amplifier, a 12 nJ seed which was generated from a self mode-locking Ti:sapphire oscillator was amplified to energy of 2.3 mJ in a pulse at 1 kHz. The spectrum of the amplifier was also measured. When the 40 nm seed was injected into the cavity, a laser output of about