  A method via the KAM technique is introduced to study the existence of
invariant tori and quasiperiodic solutions for impulsive Duffing-type equations
with time period 1. Basing on several planar symplectic homeomorphisms and some
estimates of impulsive perturbations under each symplectic homeomorphisms, we
prove via the Moser's twist theorem the boundedness (Lagrange stability) and
the existence of an invariant circle for the equation with area-preserving
impulsive terms. And this invariant circle having any rotation number
$\omega>\omega_0$ with some $\omega_0>0$, so we obtain also that the solutions
starting from the circle are quasiperiodic with frequencies $\omega$ and 1.
