According to history, migration serves as an important part of social development. It not only changed the demographic structure but also brings a strong impact to the economy. Immigration is often characterized as being either good or bad for the country. Generally speaking, the migration process is driven by "pull and push" factors; reasons for people to connect with the host country where they want to migrate and reasons that cause people wanting to leave their home country. The migration process influence both the host and the home countries in a lot of aspects. Although the pros and cons of migration on economy is complicated, it is hard to generalize some patterns. They are closely related to each other. This paper will discuss the relationship between migration and the economy in the 20th century, with two cited regions as examples: Europe and the USA and China and Hong Kong. It is noted that the host country, the United States of America, had benefited from migrants from the Southern and Eastern parts of Europe during the 1910s. For instance, job vacancies and skills gaps can be filled by the migrants. Immigrants help to address skills shortages and bring a lot of positive contributions to the economy. They provide good labor force for the host country. Among the migrants, a lot of them were young and well-trained. It is argued that that immigrants generally provide a fiscal surplus because most immigrants are young. Young European workers brought the steel and other industrial technologies to the U.S, which were vital for the American Industrial Revolution during that period. Moreover, immigrants help to fill the pension gap of the society. Young workers coming from Europe filled the pension gap by decreasing the aged population. This helps the country to maintain a healthy demographic structure. However, migration also brings negative impacts on the economy. The simple logic that the more the workers, the greater the co