Major Function-Oriented Zone Planning(MFOZ Planning) has been a strategic concern in the field of territorial development in China.In the planning,orientations of development are designed for four types of major functions,one of which is the development-optimized region.In these areas,their main orientation in the future development is industrial adjustment and upgrade,such as improving the regional ability of innovation and developing new green industries with high technology and added value.Manufacturing firm migration in these areas contains both immigration and emigration at the same time.This article takes Dongguan city in Guangdong Province as an example to analyze the mechanism of manufacturing firms in the development-optimized region.Based on the semi-structured depth interviews and questionnaire method with local authorities,industrial associations and entrepreneurs,the article demonstrates the result(s) as follow(s): Firstly,labor-intensive firm emigrations and the capital and technology-intensive firm immigration coexist at the same time.Secondly,labor-intensive firm emigration can be attributed to the factors such as rise in costs,environmental regulations,regional dependence and gaming between different local governments.Thirdly,capital and technology-intensive firm immigration can be attributed to the factors such as industrial base,regional innovation,industrial policy and soft environment.Firm migration to some extent improves the industrial adjustment and upgrade,and it will also restructure the territorial space pattern.The ecology-production-living space between the proportional relationships will also change with labor-intensive industries dispersion and capital and technology-intensive industry agglomeration.The development-optimized region will improve the quality of land space.