Abstract: The structure model of N-100 is set up on the base of structure analysis and characterization which indicate there are four kinds of carbonyl groups and five different subetitutions on the nitrogen atom Some ideal assumptions defining the structure formation of N-100 are propoed to calculate the isocyanate contat, average function degree and average relative molecular mass. Two factors affecting the accuracy of the values are discussed. Results show that the effects from different relaxation time of carbon atoms decrease as the pulse-delay increases. The similarity between calculated and values proves that the structure model of N-100 is valid.