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The objective of this research was to analyze the effect of side ventilator opening on ventilation rate based on wind factors and its effects on air temperature and relative humidity in a naturally ventilated single-span greenhouse. Front-and rear side ventilator openings are set-up in four levels: fully close, one-third open, two-third open, and fully open. Air temperature and relative humidity are observed under three levels of solar radiation intensities: less than 400 W.m-2, 400-800 W.m-2, and more than 800 W.m-2. The ventilation rate is analized using the wind pressure coefficient method by calculating the internal pressure coefficient in the greenhouse. The distribution of air temperature and air flow at constant wind speeds is depicted by CFD simulation. At all conditions of solar radiation intensities, the air temperature in the greenhouse exceeds the optimum temperature for cherry tomato plants in the generative growth phase. These indicated that the natural ventilation rate has not been able to lower the air temperature in the greenhouse for cherry tomato plants. At the constant wind speed conditions, the ventilation rate increse with increasing the ventilator opening. At a constant wind speed of 4 m.s-1, the maximum ventilation rates observed when all ventilators fully open and wind direction is perpendicular to side ventilators. The maximum ventilation rates at front-side ventilator, roof ventilator and rear-side ventilator are 0.277 kg.m-2.s-1, -0.5049 kg.m-2.s-1 and 0.228 kg.m-2.s-1, respectively.