  Many nonlinear quantum phenomena of intense laser-atom physics can be
intuitively explained with the concept of trajectory. In this paper, Bohmian
mechanics (BM) is introduced to study a multiphoton process of atoms
interacting with the intense laser field: above-threshold ionization (ATI).
Quantum trajectory of an atomic electron in intense laser field is obtained
from the Bohm-Newton equation first and then the energy of the photoelectron is
gained from its trajectory. With energies of an ensemble of photoelectrons, we
obtain the ATI spectrum which is consistent with the previous theoretical and
experimental results. Comparing BM with the classical trajectory Monte-Carlo
method, we conclude that quantum potential may play a key role to reproduce the
spectrum of ATI. Our work may present a new approach to understanding quantum
phenomena in intense laser-atom physics with the image of trajectory.
