The energy transfer reaction of metastable atom He(2³S) with molecule N2H4 was studied using discharge-flowing afterglow technique. The emission spectrum of excited radical NH(A3∏→X3∑+). NH(c1∏→a1△). NH2(A2A1 → X2B1) were observed. The ratios of formation products exit were obtained by relative spectra intensity. The emission rotational spectra of product NH(A3∏,v′= 0) were analysed,the results showed that rotational populations were " two models". The formation mechanism of excited products was: He (2³S)+N2H4→N2H4→NH(A)+ NH2(A)+H.