<正> In this paper,existing damping theories are briefly reviewed.On the basis of the existing damping theories,a newkind of damping theory,i.e.,the time-delay damping theory,is developed.In the time-delay damping theory,the damping forceis considered to be directly proportional to the increment of displacement.The response analysis of an SDOF time-delaydamping system is carried out,and the methods for obtaining the solution for a time-delay damping system in the time domainas well as the frequency domain are given.The comparison between results from different damping theories shows that thetime-delay damping theory is both reasonable and convenient.