The function of the national ecological security barrier in Three-River-Source National Park is prominent, so it is of great significance to construct and optimize its ecological security pattern. Based on the land use and remote sensing data in 2020, and the morphological pattern spatial analysis method (MSPA), we constructed the ecological sensitivity evaluation system. In addition, we extracted the important ecological corridors and potential ecological corridors to form the ecological security pattern of Three-River-Source National Park. The functions of the ecological security pattern were optimized using the minimum cumulative resistance model and the gravity model. The results are as follows: (1) The ecological source area of Three-River-Source National Park was 26 833 km2, accounting for 21.80% of the total area. (2) A total of 9 important ecological corridors (536.62 km) and 55 potential ecological corridors (6 080.15 km) were extracted, among which 45 potential ecological corridors (5 124.17 km) and 8 important ecological corridors (522.10 km) were extracted from the Yangtze River Source Park and Lancang River Source Park. Meanwhile, 10 potential ecological corridors (955.98 km) and 1 important ecological corridor (14.52 km) were extracted from Huangheyuan Park. (3) Optimization of the ecological functions of Three-River-Source National Park results in a core protection area (39 613.58 km²), an ecological conservation area (67 261.84 km²), a recreation exhibition area (10 143.44 km²) and a traditional utilization area (6 081.34 km2), accounting for 32.18%, 54.64%, 8.24%, and 4.94% respectively. The results provided reference value for the spatial planning of Three-River-Source National Park and future function optimization of national ecological security barriers.