In the main control rooms of nuclear power plants (NPPs), operators frequently switch between alarm displays and system-information displays to incorporate information from different screens. In this study, we investigated two integrated designs of alarm and process information - integrating alarm information into process displays (denoted as Alarm2Process integration) and integrating process information into alarm displays (denoted as Process2Alarm integration). To analyse the effects of the two integration approaches and time pressure on the diagnosis performance, a laboratory experiment was conducted with ninety-six students. The results show that compared with the non-integrated case, Process2Alarm integration yields better diagnosis performance in terms of diagnosis accuracy, time required to generate correct hypothesis and completion time. In contrast, the Alarm2Process integration leads to higher levels of workload, with no improvement in diagnosis performance. The diagnosis performance of Process2Alarm integration was consistently better than that of Alarm2Process integration, regardless of the levels of time pressure. Practitioner Summary: To facilitate operator's synthesis of NPP information when performing diagnosis tasks, we proposed to integrate process information into alarm displays. The laboratory validation shows that the integration approach significantly improves the diagnosis performance for both low and high time-pressure levels.