Amplification of matter waves was analyzed in an angular condition of resonant light diffraction by a Bose gas released from an optical lattice.We found that competition between superradiant scattering Fig l(a) 、 (o)and matter wave amplification Fig 1(c)、 (d) which will be dominated while the optical potential depth increases.The first order mode can be amplified and related distribution of momentum 〈p〉 will be oscillated vs the delay time between switch off the optical lattice and switch on the pump laser pulse, see Fig 2.The curve shows the correlation between wave functions of different on site of optical lattice.The energy gap of Bloch bands in one dimensional optical lattice can be measured also by similar approach.