Based on the expended model of North-South technology diffusion,this paper analyzes the issue of technology catching up in lagging countries which carry out independent innovation and imitation at the same time.We conclude that at the early stage of technology progress,loose IPRs in lagging countries are helpful for technology catching up,but strict IPRs are benefit for technology progress in the long run.Whether a lagging country can catch up the leader depends on the inputs and efficiency of independent innovation.The developing experiences of Japan,Korea and India also validate the theory.Its policy implement is obvious: lagging countries have to increase the inputs and efficiency of independent innovation to catch up the leader.