The existing molecular cloning methods are often limited by the availability of suitable restriction sites. It is still a challenge for simultaneous cloning of multiple fragments into different sites of a single vector. Here we developed a novel method named improved overlap extension PCR (IOEP) for restriction enzyme independent cloning of large fragments. The addition of primers enables IOEP to exponentially amplify the overlap extension product, thus greatly improves the amplification efficiency of large fragments. Moreover, coupled with the benefit of T4 DNA polymerase to improve cloning efficiency, our method can be used to simultaneously insert, delete and replace multiple DNA fragments at different sites.