In this paper, we give a new proof of the scattering and blow-up theory of the two coupled nonlinear Schrödinger system via establishing the corresponding interaction Morawetz estimate and scattering criterion. The method of this paper simplifies the proof in Xu, and the result of the paper improves the result in Xu. KEYWORDS blowup, coupled NLS system, Morawetz estimate, scattering MSC CLASSIFICATION 35L70; 35Q55