Abstract: To overcome disadvantage of Levenberg-Marquardt(LM) algorithm,which can not keep geometric correlation of defect parameters,a modified method with fast convergence is presented.In a heat transfer model for a two-dimensional test piece with a subsurface rectangular defect,numerical experiments are conducted to verify effectiveness of the modified LM algorithm.Factors of initial guess and infrared temperature measurement error are considered.Conclusions are drown as follows: The modified LM algorithm keeps geometric correlation of defect parameters well and influence of initial guess is negligible;Identification accuracy of different defect parameters differs due to infrared temperature measurement errors.