Abstract: Aiming at plastic greenhouses' safety and economic problems in middle reaches of Yangtze River, wind load and snow load in Changsha City, Hunan Province were selected as case studies．A 12 m single-pipe shoulder plastic greenhouse arch frame was chosen as research subject, and structure's strength, stiffness and stability indexes under various load combinations were analyzed by using ANSYS finite element software to establish model, and obtain the most unfavorable load combination．On this basis, influence of different connection forms at arch frame joints on structural safety was studied, while arch cross-section and structural design were optimized．Additionally, impact of varying spans on material consumption was analyzed．Results showed that structural stiffness would increase, internal force distribution would be more uniform after converting arch frame joints from hinged to fixed connections．This reduced both maximum stress and maximum deformation, effectively improving structural safety．Structural optimization achieved by adding tie rods to arch frame reduced internal forces, and material consumption for single-span frame could be reduced by 15.1% while meeting safety requirements, thereby economic goal was achieved．Compared to 12 m span arches, 10 m and 8 m span arches reduce amount of material used per unit horizontal projection area by 14.5% and 22.7% respectively, and reduce amount of material used per unit volume by 18.4% and 18.7%, respectively．Under premise of ensuring functionality and safety while balancing economic consideration, it was suggested that plastic greenhouses' arch frame span in middle reaches of Yangtze River should be selected as 10 m．