The embodiment of the invention provides a method and apparatus for calculating a service delay, and relates to the field of communication. The delay of the service can be accurately reflected. The method comprises the following steps: determining, by a computing device, the number N of all multiplexing sections in an ROADM network, wherein N is an integer greater than 2; determining, by the computing device, N services; for the first service and the second service in the N services, at least one multiplexing section corresponding to the first service is not exactly the same as the at least one multiplexing section corresponding to the second service, and the first service and the second service are any two services of the N services; and determining, by the computing device, the delay ofeach multiplexing section in all multiplexing sections according to the delays corresponding to the N services and the multiplexing sections corresponding to the N services. The method and apparatus provided by the invention are applied to the ROADM network.