Abstract: As a branch of infrared nondestructive testing,Vibrothermography(VT) has special advantages in the detection of micro-cracks.But the heat generation process is very complex to describe,as a result of which detection process is rather addicted to subjective experience.This article describes the heat generation of VT by using a two-degree-of-freedom model with concentrated masses.For a micro-crack in aluminum alloy beam,the internal heat source at the crack is described by an equivalent viscous damping,and the heat transfer is considered using a semi-infinite model.The results show that the factors such as frequency and amplitude of exciting force,the location of cracks,materials could influence the heat generation and concrete influence rules are given which provide reference for optimizing the detection condition.