Abstract: As an important model for promoting agriculture and clean energy synergistic development, photovoltaic greenhouses have been widely implemented in regions such as Yangtze River Delta．However, shading effect of photovoltaic modules significantly impacts light environment inside plastic greenhouses, restricting normal crop growth, and necessitating systematic evaluation and structural optimization research．Thus, a photovoltaic-integrated east-west oriented multi-span greenhouse in Huai'an City, Jiangsu Province, was selected as research subject．A three-dimensional light environment model was constructed by integrating field-measured illumination data with numerical simulation techniques to assess effects of different photovoltaic module arrangements on internal lighting rate and light illumination distribution．Results showed that under current dense photovoltaic module layout on southern roof, average lighting rate was only 11.6%, significantly lower than 39.0% observed on northern roof．Constructed light environment model exhibited high consistency with measured data, with a daily average lighting rate simulation error less than 5.5%, indicating excellent applicability．Based on this, simulations of different module spacing strategies revealed that increasing spacing from 0 cm to 60 cm improved southern roof's lighting utilization rate by 6.7 percentage points．Furthermore, light distribution became more uniform, significantly enhancing illuminance levels in greenhouse deeper areas．It is recommended to adopt 40 cm to 60 cm module spacing as an optimal strategy to enhance the combined benefits of agricultural productivity and photovoltaic power generation efficiency．Theoretical support for planning design and structural optimization of photovoltaic-integrated agricultural systems was provided by research findings．