Abstract: The reactivity feedback effect of metal burst reactors is mainly caused by thermal expansion. The method of waveform calculation was built with MC neutron transport code, the thermomechanics program and point reactor neutron kinetics equations on the basis of reactivity temperature coefficients. The coupling relation between heat power and reactivity is got by means of the three-dimensional MC neutron transport code and thermomechanics program. The waveform is got by way of solving point reactor neutron kinetics equations including the coupling relation. Using this convenient method, the typical waveform of Lady Godiva was calculated, and the calculated results are consistent with the experiment results of LANL.