The electron energy distribution function (EEDF) of weakly ionized air plasma (79% nitrogen and 21% oxygen) is investigated by solving the Boltzmann equation with the spherical harmonics expansion. It is found that the EEDF deceases sharply in an energy range from 2 to 3 eV for low reduced field (*E/N* < 100 Td), and the high energy tail of the EEDF decreases more sharply than Maxwell distribution. When the reduced field increases to a range 400 to 2000 Td, the EEDF approaches to Maxwell distribution. When the reduced field is greater than 2000 Td, the high energy tail (>200 eV) of the EEDF deceases more slowly than Maxwell distribution. It is shown that the EEDF approaches to Maxwell distribution in a high frequency field. The effective electron temperature is dependent only on *E/ω* for *ω* >> *v _{m}*, but on