Studies on simple atoms and molecules in ultrafast intense laser field explore abundant physical phenomena and provide basic physical information for extreme physical processes under the condition of high energy density.We mainly introduce some experimental and theoretical studies on polyatomic molecules in a femtosecond laser field from our laboratory recently,including ionization/ dissociation of polyatomic molecules in femtosecond laser,ultrafast energy transfer of excited molecules in solutions,and controlling the ablation by shaped femtosecond pulsed laser.