The cooling effect is an important ecosystem service provided by urban green space. However, the quantitative information linking vegetation type and cover with cooing effect is lacking in Southern China cities such as Shenzhen, where summer heat is extremely strong. Here we chose three residential quarters in Shenzhen, and divided each residential quarter into twenty-five 20 m×20 m quadrats to study the relationship between near-surface air temperature and green space vegetation characteristics, including the size of green space, the dominance of trees in the overall vegetation composition. We evaluated the Tridimensional Green Biomass (TGB) in each 20 m×20 m quadrat according to the method of reference literature based on the field vegetation survey of the selected residential quarters. We also collected meteorological data at the centre of each quadrat from late August to early September. To avoid the influence of light exposure, the meteorological observation points were selected under the shade of vegetation in each quadrat. In each residential quarter, meteorological observations were taken three times a day from 12:00 to 13:00 in two consecutive days, and we took the average of the six results to present the general microclimate conditions of the time period from 12:00 to 13:00. Finally, using 25 quadrats of each residential quarter as sample units, we carried out a statistical analysis to find out the relationship between vegetation amount (TGB) in quadrat and the average temperature. In particular, we fitted a non-linear curve between T and TGB, and between the cooling effect (ΔT) and TGB.Our results showed that: (1) logistic curve can accurately describe the relationship between TGB and temperature, and the relationship between TGB and the cooling effect (ΔT), with adjusted R² of 0.88, suggesting that the cooling effect is strongly related to the amount of all vegetation in the 20 m×20 m area. And if the vegetation cooling effect is to be considered in a residential green-space design, total green space and amount need be considered.(2) Our calculations showed that when the urban heat effect is high (temperature is from 36℃ to 39℃; relative humidity is from 52.9% to 65.4%), TGB in quadrat must reach 200 m³ to exert appreciable cooling effect; and when TGB is more than 300m³, the cooling effect would reach its maximum.(3) The significant correlation between ΔT and TGB of different vegetation composition showed that the TGB of trees is related to ΔT, but the TGB of shrub-grass was not, suggesting that the shading effect from trees plays a major role in the overall cooling effect of the vegetation.In summery, by examining the relationship between vegetation amount and the cooling effect of the vegetation, we acquired the quantitative information on how to design green space in urban residential area so that desired cooling effect can be achieved. We suggest that in green-space design in Shenzhen, the area must be large enough (20 m×20 m), and the green space must be dominated by trees.