A time delay adjustment method is provided, which includes the following steps. A same scrambling signal is added into two received signals. The added scrambling signals are then extracted. A delay difference between the two signals is detected according to a difference between the two extracted scrambling signals. The delay difference between the two signals is adjusted by delaying one or both of the two signals. Furthermore, a time delay adjustment device and an optical transmission apparatus are also provided. Therefore, time delay can be adjusted online, and real-time monitoring and adjustment of delay difference is also achieved.