This study explores the factors that affect the size of typhoons. We analyzed environmental factors and wind field structures, and used experiments to simulate wind fields and rainfall patterns. Based on 358 typhoons in the Northwest Pacific from 2010 to 2024, the radius and intensity of typhoons show a positive relationship. According to this relationship, typhoons were divided into large and small types to make the definition more objective. The results show that large typhoons occur most often in August, and small typhoons occur most often in September and November. In October, the number of typhoons is small, but their average radius and intensity are the highest. The location where a typhoon forms also affects its size. Large typhoons usually move west and then turn north, and their radius becomes larger when their intensity decreases. Small typhoons often move west at low latitudes. Structurally, large typhoons are more symmetric and have higher strength, while small ones are less symmetric and often have strong winds on one side. When westward typhoons cross Taiwan’s mountains, their radius becomes smaller, and both intensity and strength drop clearly. Rainfall mainly appears on the windward side. In the airflow model with mist, the results show that stronger suction, smaller inflow angle, and more symmetric wind fields create larger typhoons. A Taiwan-shaped obstacle was added to simulate the terrain effect, and a cellulose sponge was used to test rainfall simulation to verify the analysis results.