The disclosure discloses a de-mapping method and a device for an Optical Transport Unit (OTU) frame. The method includes: setting a receiving reference clock and a de-mapping path according to a highest priority of an OTU frame mapping mode of a local device (S102); receiving an OTU frame of an opposite device by using the receiving reference clock and the de-mapping path (S104); determining a de-mapping priority of the OTU frame according to a clock recovery result of the received OTU frame and a customer service alarm instruction (S106); and de-mapping the OTU frame of the opposite device by using a receiving reference clock and a de-mapping path corresponding to the determined de-mapping priority of the OTU frame (S108). By means of the present invention, the de-mapping efficiency and accuracy of the OTU frame in an optical transport network are improved.