Embodiments of the present invention disclose a service transmission processing method, a node device and a network system are provided. One method includes: receiving service data after relay processing by a 3R relay node, where the relay processing includes terminating and regenerating an Optical Channel (OCh) of the service data, and when the OCh is terminated, transparent transmission is performed on an Optical channel Transport Unit (OTU); and performing defect detection on a path of the OTU to obtain a detection result of the path of the OTU. Another method includes: obtaining an overhead in an Optical Transport Network (OTN) frame; and judging whether the overhead includes a Client Signal Fail (CSF) inserted after a signal fails, and if the overhead includes the CSF, determining a path where a defect occurs according to the CSF.