Abstract: Agricultural engineering is a foundation of agriculture and guarantee for realizing agricultural modernization, which generally refers to agricultural engineering technology, agricultural engineering discipline and agricultural engineering construction. With the expansion of agricultural engineering service objects as the main line, this paper analyzes the development process and characteristics of agricultural engineering in typical countries and regions such as the United States, Europe and East Asia, and extracts and summarizes the general rule of the development of agricultural engineering in the world. According to this rule, deductive reasoning is made on the development status and the current stage of China’s agricultural engineering, and the enlightenment is summarized in combination with China’s national conditions and rural revitalization needs. The results show that according to the expansion of service objects, the world's agricultural engineering has experienced the evolution of four stages: Agricultural engineering technology stage serving simple agricultural production; occurring and development stage of agricultural engineering discipline mainly serving agricultural production; the stage paying equal attention to agricultural production and rural construction; biological system engineering stage with the service object expanded to biological system; the development of agricultural engineering in the world is characterized by focusing on production in the early stage and paying equal attention to production and life in the later stage. Its development is greatly affected by the development of other science and technology, and the driving force of change comes from social needs. Combined with the stage and characteristics of China’s agricultural and rural development, as well as the common development strategy of agriculture, rural areas, and farmers, the inspiration for China from the development laws of world agricultural engineering is that currently China should vigorously develop the agricultural engineering that focuses on both agriculture and rural areas development, which is in the third stage of agricultural engineering development; and China should also promote the development of biological system engineering, that is to promote agricultural engineering towards the fourth stage. This study explores and summarizes the development laws of agricultural engineering in the world based on service object expansion, which can provide reference for a comprehensive understanding of the direction and trend of agricultural engineering development in China.