A route diagnosis method which supports policy-based routing is applied in the network which includes a router supporting policy-based routing, which comprises: adding stream description information of service stream in diagnosis-protocol-message, and containing a router warning option in IP head of the said diagnosis-protocol-message; based on the router supporting policy-based routing receiving said diagnosis-protocol-message, routing according to said stream description information in the said diagnosis-protocol-message; said diagnosis-protocol-message is processed as standard diagnosis-protocol-message by the router which is independent of policy-based routing. Employing the method of the present invention, the middle router which supports policy-based routing is able to transfer the message independent of IP head of the said diagnosis-protocol-message, but select routing according to said stream description information included in the message, thereby being capable of keeping the consistency between the diagnosis-protocol-message and routing of the service stream. The purpose that is actually diagnosing routing or correctly diagnosing route is achieved.