The scalability has remained a challenge in the design of distributed publish/subscribe systems. In this paper we propose a novel solution to address this problem in contentbased pub/sub systems on top of Distributed Hash Table. The main objective is to ensure an appropriate amount of rendezvous point nodes in the system, as well as maintain an even load distribution among them. An attribute-vector based publish/subscribe scheme and related load balancing mechanisms (ID space partitioning, attribute grouping, dynamic ID space split-merge) are proposed to achieve this goal. The experimental results show that our approaches can achieve a good scalability by efficiently distribute/ balance load among an adaptive quantity of rendezvous point nodes, while retaining very small overhead and latency.