Multi-path routing in the optical burst switching(OBS) networks can reduce the burst loss probability(BLP) by distributing the data burst traffic to multiple paths, compared with single path routing. Unlike the other multi-path routing schemes without considering the carrying capability of the routes, a new multi-path routing scheme based on effective voids(MPEV) is proposed to balance the load of multi-path and reduce the BLP in the paper. MPEV scheme first obtains the information on effective voids of the bottleneck link of multipath by sending a probe packet periodically. The effective voids can accommodate data bursts and accurately represent the available channel resource that is the main determinant of the BLP for OBS networks without optical random access memory. Then MPEV scheme distributes the burst traffic between an ingress node and an egress node to multiple link-disjoint paths by the ratio of the effective voids. More traffic is distributed to the path that has more effective voids, and vice versa. And the distributed amount is proportional to the effective voids of the bottleneck link. So MPEV scheme can balance the load of multi-path routes and can effectively reduce the BLP by avoiding the high load of a single path. And it is easy to implement and agilely adapt to dynamic network traffic. The performance of MPEV scheme is analyzed by queuing theory and is evaluated by simulation. The numerical results show that the proposed scheme can effectively reduce the BLP and balance the traffic load over multiple paths at the same time. Multi-path routing in the optical burst switching (OBS) networks can reduce the burst loss probability (BLP) by distributing the data burst traffic to multiple paths, compared with single path routing. Unlike the other multi-path routing schemes capability of the routes, a new multi-path routing scheme based on effective voids (MPEV) is proposed to balance the load of multi-path and reduce the BLP in the paper. MPEV scheme first obtain the information on effective voids of the bottleneck link of multipath by sending a probe packet periodically. The effective voids can accommodate data bursts and accurately represent the available channel resource that is the main determinant of the BLP for OBS networks without optical random access memory. Then MPEV scheme distributes the burst traffic between an ingress node and an egress node to multiple link-disjoint paths by the ratio of the effective voids. More traffic is distributed to the path that has more effect And the distributed amount is proportional to the effective voids of the bottleneck link. So MPEV scheme can balance the load of multi-path routes and can effectively reduce the BLP by avoiding the high load of a single path. And it is easy to implement and agilely adapt to dynamic network traffic. The performance of MPEV scheme is analyzed by queuing theory and is evaluated by simulation. The numerical results show that the proposed scheme can effectively reduce the BLP and balance the traffic load over multiple paths at the same time.