Abstract: The second-order nonlinear system with delay x"(t)+f(x(t),x'(t))+g(x(t),x'(t))ψ(x(t-τ))=p(t) being considered. Four theorems on the stability of zero solution, the boundedness of the solutions, the existence of the periodic solutions, the existence and uniqueness of the stationary oscillation are obtained by means of the Liapunov’s second method. The conclusion in the literatures are generalized.