The interconnection network plays an important role in performance and energy consumption of a Network-on-chip(NoC) system. PRDT(2,1) is a promising solution for the interconnection network of NoC due to its smaller diameter and average distance, constant node degree and full scalability. In this paper, a binary routing algorithm for PRDT is presented in order to improve the performance of routing for PRDT with small size. In the case that PRDT consists of no more than 16 nodes, the binary algorithm is deadlock-free without the utilization of virtual channels. Based on the binary algorithm, it proposes a fully adaptive routing algorithm which is deadlock-free by using a few virtual channels. The comparison between the deterministic, adaptive binary algorithm and the original vector algorithm is conducted in a simulation. The results show that the binary algorithm is better in performance while its hardware cost is lower. So the algorithm is readily applicable to the small PRDT-based NoC systems.