Abstract: Two kinds of methods for implementing time reversal of electromagnetic signals in time domain based on digital signal processing and analog signal processing are introduced and discussed. The former technique can directly sample and process time domain signal, or use phase conjugation in frequency domain, to implementing time reversal of electromagnetic signals; while the other technique is based on the principle of temporal-imaging to implement time reversal of electromagnetic signals in time domain, including two schemes of microwave photonics technology and fully electronic technology.