As an important protection barrier of the ecosystems in the four provinces, including Tibet Autonomous Region, Sichuan Province, Qinghai Province, and Gansu Province of western China, it is of great significance to evaluate the conservation effectiveness of the natural reserves located in the four provinces of western China to promote the construction process of ecological civilization. However, there are currently few comprehensive studies evaluating the effectiveness of natural reserves in the four provinces of western China with consideration of different protection levels and objectives. The objectives refer to the ecosystems characterized by the wild animals, wild vegetations, forests, inland wetlands, and desert. To address this issue, this study systematically evaluated the effectiveness of the natural reserves located in the four provinces of western China by applying two methods, i.e., trend analysis and stability indicators, to the kernel Normalized Difference Vegetation Index (kNDVI) data derived from the GIMMS NDVI product. Such evaluation was conducted from both temporal (before and after the natural reserve establishment) and spatial (inside and outside the natural reserves) dimensions with consideration of the different protection levels and objectives. Results show that (1) vegetation growth in the natural reserves of the four provinces in western China exhibited an upward trend over the past 40 years (from 1982 to 2022), and the trends of vegetations in the eastern regions were typically higher than those in the western regions; (2) protection effectiveness of the natural reserves is significant and remarkable. Although vegetation stability decreased after the reserve establishment in 70% of the total pixels, trend of vegetation growth increased in 52% of the total pixels. Moreover, vegetation growth trend and stability inside the natural reserves were better than those outside; (3) national-level inland wetland reserves were superior to provincial-level ones. Temporal analysis showed that provincial-level wildlife reserves were better than the national-level ones. In addition, reserves with national-level forest ecosystem were better than the provincial-level ones. Nevertheless, evaluation results of the spatial analysis were opposite when compared with those of the temporal analysis. (4) the upgrade of the protection level of a natural reserve, i.e., from provincial level to national level, has a positive impact on its conservation effectiveness. The conservation effectiveness during the nation-level-based period is superior to that during the provincial-level-based period. Our study provides a basic reference to improve the natural reserve management and our results can promote ecological civilization for natural reserves located in the western China.