Heat loss in steam injection pipelines is one of the primary causes of low thermal efficiency in heavy oil steam injection. To investigate the heat loss and heat transfer variation patterns in steam injection pipelines, a three-dimensional numerical model was established using Fluent software. The effects of overhead pipeline insulation parameters and environmental factors on heat loss and radial temperature distribution were analyzed. This study systematically quantifies the effects of sunlight radiation for the first time and proposes a heat loss correction equation for sunlight conditions. Additionally, overhead and buried pipelines were compared within the same modeling framework. The results show that selecting insulation materials with low thermal conductivity and increasing the insulation thickness can effectively reduce steam pipeline heat loss. For overhead pipelines, as sunlight radiation intensity increased from 0 W/m² to 800 W/m², actual heat loss decreased from 68.43 W/m² to 58.03 W/m². A sunlight-dependent effective heat transfer coefficient, h_Sunlight (E, T), was fitted to extend surface temperature heat loss calculations under sunlightt conditions, in which determination (R²) is 0.9951 and the average error is 5.57%. Under the same operating conditions, the heat loss of the buried pipelines was 62.59 W/m², which was 8.5% lower than that of the overhead pipelines. The findings provide a theoretical basis for the insulation design, thermal efficiency assessment, and operational optimization under sunlight radiation conditions of steam injection pipelines.