Abstract: Human activities have become a significant factor affecting the ecological status of protected areas (PAs). Current research mainly focuses on the overall monitoring of human activities within PAs, but studies on the specific impact of agricultural activities remain insufficient. This paper selected the Shandong Rongcheng Whooper Swan National Nature Reserve as the study area, and utilized remote sensing datasets of cropland change to examine the effectiveness of the reserve′s effectiveness at resisting the pressure of cropland expansion. This study employed methods such as inside-outside comparison, land utilization transition matrix, and the human activity interference index. The results indicate that: (1) Current Status: In 2020, cropland within the reserve accounted for 26.93% of the total area, primarily distributed in the central region, i.e., the boundary of the buffer zone and the main area of the experimental zone. (2) Temporal-Spatial Dynamics: From 1980 to 2020, the cropland area in the reserve showed a general decreasing trend, mainly in the core and buffer zones, while cropland in the experimental zone showed an overall increasing trend. (3) Conservation Effectiveness: Between 1980 and 2020, the growth rate of cropland area inside the reserve was lower than that outside, indicating relatively better conservation effectiveness. (4) Impact Intensity Evaluation: The human activity interference index within the reserve showed a decreasing trend from 1980 to 2020, demonstrating the reserve′s effectiveness at resisting the pressure of cropland expansion. This study′s findings can provide scientific support for the monitoring and management of nature reserves.