Based on calculating the influence of RF-field with various physical parameters on the dynamics of the spin 1/2 system,it was found that the spin state could be changed up and down by choosing appropriate RF pulses,and the coherent control of the RF pulses could substantially modify the behavior of spin dynamics:quicker change of two states could be produced even for small pulse duration.In addition,the oscillatory structures around the resonant frequency and the propagation features of the pulses depend on the relative phase of the biehromatie RF pulses.