Abstract: Taking the thermal discharge of Kemen power plant in Luoyuan Bay as the research object, the influence of the Kemen power plant thermal discharge on the water temperature rise in Luoyuan Bay was studied based on field observation and numerical simulation. The range of the maximum temperature rise envelope in the observation period was measured by field measurements of water temperature in the study area. The planar distribution and vertical variation characteristics of temperature rise were analyzed, and the maximum temperature rise envelopes were presented. Results showed that the planar distribution of temperature rise was related to the tidal current characteristics and coastline topography of the sea area. The surface water with temperature rise diffused basically along the upstream and downstream of the power plant parallel to the coastline, after the thermal discharge of the power plant into the sea. The diffusion distance along the coast direction is far greater than that in the offshore direction. The area with the largest temperature rise was near the outfall. The temperature rise decreased along the offshore and coastal directions, and the decrease was faster in the offshore direction. Temperature rise occurred mainly in the surface water, and the influence area decreased rapidly in the vertical direction. Below 3 m of water surface, the temperature rise was less. Tidal range played a role in the diffusion trend and scope of water temperature. Generally, the smaller the tidal range was, the larger the diffusion area of temperature rise was.