Based on the equation of Navier-Stokes and with computational fluid dynamic software CFX, a 3-D steady simulation of natural ventilation was performed in the multi-span plastic greenhouse that was equipped with inner solar-shading screen. Outside wind direction was assumed to be parallel to the greenhouse ridge. Result showed that the airflow velocity decreased remarkably in two side-spans, and it was about one sixth of the outside and less than half of airflow velocity inside the greenhouse without inner screen. Flow state inside the middle span did not seem to change much except for a bit of shift in the direction of right side-span. The airflow uniformity was somewhat improved in left side-span, while the average velocity decreased and circumfluence was not so obvious. The static area occupied less space, especially in the lower part of greenhouse. In the left side-span, the airflow gathered among the middle and upper area of greenhouse, while the uniformity was improved a little. The frontispiece door and side-opens played an important role in affecting the airflow pattern inside the greenhouse, the airflow movement above solar screen strengthened by the effect of top-windows.