A method and an apparatus for locating a fault cause are provided. The method includes: obtaining parameter values of a plurality of running parameters and a parameter value of a fault parameter in preset duration before a wavelength division multiplexing board device is faulty; determining a correlation between each of the plurality of running parameters and the fault parameter; and determining at least one target parameter from the plurality of running parameters based on a value of the correlation, where a correlation between each of the at least one target parameter and the fault parameter is greater than a correlation between the fault parameter and a running parameter other than the at least one target parameter in the plurality of running parameters. Accuracy of locating a fault cause can be improved in the embodiments of the present disclosure.