Path protection with differentiated reliability is a very promising survivable scheme in optical networks. It can meet the requirement of network traffics with different reliability demand in a resource efficient manner. This issue has been researched mainly in single-domain optical networks, however, its achievement can not be applied to next generation optical network directly, which is accepted to be a multi-domain optical netwrok. Therefore a path protection algorithm with differentiated reliability in multi-domain optical networks is proposed in this paper. And its performance is evaluated through simulation, which verifies that the algorithm can not only meet the reliability demand of different traffics in multi-domain optical networks, but also improve the network resource efficiency and reduce the traffic blocking probability.