If We mix the microsample to be determined and the standard sample with known δ value, We Can deduce the calculation formulae for mining of different ratios or equal ratio according to equilibrium relationship before and after the mixing: δsA=(δSA + re -Xreδ)/XSA or δSA=2δSA + re -δre Based on this principle, the author advances a new stable isotope analytical method for mixed model of microsa mples (carbon, nitrogen, oxygen and sulfur). Experiments shnw that if onlv the hiehlv pure microsa male is mixed with the standard sample and the operation procedure is correct, the d value obtained will meet the require ment of accuracy.This suggests the feasibility of this method. The present paper reports for the first time in China the δ15N value of atmosphe- ric nitrogen,which is entirely coasistant with the internationally established conclusion that δ15N value of the atmospheric nitrogen is zero.Finally,some problems worth further consideration are pointed out.