This work studies the application of differential space time block code (STBC) for wireless multi-hop sensor networks in fading channel. We select multiple sensors as parallel relay nodes to receive and transmit signals from the previous hop. These relay nodes do not exchange symbols with each other but forward the symbols in parallel to the destination using STBCs. The proposed technique has low complexity even when the number of parallel relays grows, since it does not need to track or estimate the time-varying channel coefficients. The steady state network performance measures, such as network throughput and transmission delay, are analyzed via Markov chain modelling. Compared to the traditional single relay routing method, our proposed method offers improved performance.