In order to study the effect of laser peening on the properties of titanium alloy, a TC4 titanium alloy sample is processed using YAG laser with the wavelength of 1064 nm, pulse energy of 0～6 J and pulse width of 6～14 ns, and its micro-hardness and residual stress are examined and analyzed. The experimental results show that the satisfying laser peening appearance can be achieved when the pulse energy is 6 J, pulse width is 12 ns and tamping layer thickness of water is 1.8 mm, the surface micro-hardness increases up to 33.5% and the compressive residual stress on the surface of laser shocked area reaches -323 MPa. Laser peening improves the hardness and residual stress of titanium alloy significantly. The experimental results show that the effect of laser peening evidently strengthens the titanium alloy.