Under the decoding and forwarding mode,traditional differential network coding schemes involve complicated procedures of detection and re-coding at relay nodes. To solve this issue, a differential network coding scheme with symbol multiplying in complex field is presented. Consequently, two relay detection methods are proposed, which can reduce the detection and recoding complexity significantly at relay nodes. In order to achieve the high order diversity gain, the proposed differential network coding is extended to multi-relay setting. As a result, a differential random space-time network coding scheme is presented, where the cooperative diversity order that can be achieved is equal to the activated relay number. The analysis and simulation results validate the proposed differential network coding schemes in both single  and multi-relay settings.