Studies of the response of stomatal behavior to environmental factors were conducted. It is shown that light intensity and atmospheric vapor deficit (△e) are major factors having influence on the stomatal behavor.The diurnal trend diagram of the stomatal resistance is shaped as "W"regardless of weather types, while the maximum of the resistance atnoon its greater on sunny days than on overcast day. The whole diurnalprogram is divided into three portions: OPENING-RESPONDINGperiod, MIDNOON-REST period,and CLOSING-RESPONDING period.The diurnal shape of the resistance curve is determined by circadianrhythms and environmental factors. The resistance is higher in thelower layer than in the upper layer in the general functional formГ_s=Г₀ f(I) g(△e)…. The special forms of the individual periods are as follows: 1) OPENING-RESPONDING period and CLOSING-RESPONDINGperiod Г_s=Г₀ exp(-a₁I) (1+b₁△e) 2) MIDNOON-REST periodГ_s=1/2{ [(Г_max-Г_min)/2] cos (2π(t-t₀)/T)+(Г_max+Г_min)} exp(-a₂I) exp (b₂△e)