As an important method of reservoir parameter calculation and single well controlled reserves evaluation, production decline analysis has been widely used in conventional and unconventional reservoir evaluation and dynamic reserve calculation. However, researches on heavy oil reservoir production decline analysis model have rarely been reported. Therefore, based on the unsteady seepage theory, an unsteady mathematical model of radial composite reservoir with Newtonian and power law fluid is established to get NPI and Blasingame production decline characteristic curves. The results show that the characteristic curves can be divided into four flow stages, including Newtonian fluid radial flow stage, transition flow stage, power?law fluid radial flow stage and pseudo?steady?state flow stage. The NPI integral derivative curve of power?law fluid radial flow stage is a straight line with slope of (1-n)/(3-n). The higher the power?law index and mobility ratio indicates the larger value of power?law fluid flow phase curve. The accuracy of the model is verified by fitting the measured data from Liaohe Oilfield.