Abstract: A new formalism was proposed to describe the evolution of density operators in multi-pulse NMR experiments for the strongly coupled AB spin systems(I=1/2); The evolution formula of spin operators were derived.The polarization transform INEPT experiment and two-dimensional DQ-INADEQUATE experiment were deseribed. The formalism is distinct on physical meaning and requires less ealculation.

Key words: Strongly coupled AB systems, NMR experiments, Density operator foimalism