Highorder correction to the fields of ultrashort, tightlyfocused laser pulses expressed in power series of ε=1/(ω0t0) and s=1/(k0w0)（ω0=ck0 the central oscillatory frequency, t0 the pulse duration, w0 the beam waist radius), are derived. Based on paraxial approximation, the firstorder correction terms to the Gaussian pulses are explicitly given. Their corrections of amplitude and phase, are found to be related to the variable of ε. Applying them to the study of the electron dynamics in the intense laser pulse field, we found that as long as ω0t0>20, the zerothorder approximation (long pulse approximation) is adequate for describing the interaction. For ω0t0<20, higherorder corrections have to be taken into account.