Based on Nolle's consideration, a new model is proposed which involves the resistance of environmental gas to vibrating, the change of reduced mass caused by environmental gas and the nonlinearity of dynamic modulus of sample. From this new model, equations were developed for plotting theoretical resonance curves and phase difference curves under various environmental gas pressures, and other equations were also derived for calculation of nonlinearity of dynamic modulus in addition to initial dynamic modulus and dynamic viscosity.To discuss the applicability of this model, a stable vibrating provision and a sensitive measuring system were made. For each sample, resonance curves and phase difference curves were recorded under various environmental gas pressures. As the curves obtained from measurement coincided well with those theoretical ones, it became known that the vibrating behaviours of different kinds of macromolecular reeds can be described and the nonlinearity of dynamic modulus can be evaluated with this new model under various environmental gas pressures.