Abstract: In the implementation of the Three Lines One Permit environmental management mechanism process, scientific delineation and effective management of ecological space is an essential part of planning environmental impact assessment (PEIA). Based on the four main stages of urban planning (i.e. outline formation, planning research, planning drafting, and planning approval), the main technical processes of ecological space optimization and management for PEIA were constructed, including the main tasks of spatial element analysis and basic scheme formation, analysis of the ecological environment and spatial coordination, evaluation of the impact of planning on spatial utilization, and recommendations for spatial optimization and management. The technical processes were also applied to the Environmental Impact Assessment of Shanghai Baoshan District Master Plan. The results showed that by incorporating ecological protection red lines and river networks as well as adding new ecological nodes and corridors, the total optimized ecological space in Baoshan District increased from 65.74 km² to 121.84 km², accounting for 40.4% of the regional land area, meeting the requirements of Shanghai Urban Master Plan (2016-2040), which proposed that by 2040, Baoshan District's ecological land would account for 40% of the land area. In conclusion, urban PEIA could further optimize the ecological spatial pattern in terms of major ecological environmental issues and regional environmental demands based on the ecological space of urban planning, and provide effective means to promote new urbanization and ecological civilization construction in China.