Aiming at spherical dual-porosity reservoir, an unsteady seepage model that based on the three different kinds of outer boundary (infinite, constant value and closed) conditions was established in this paper. Using the Laplace transform method, similar structure of dimensionless bottom pressure solution in the Laplace space and similar nuclear function were obtained. This is not only providing us a new road to further explore the inherent law of the solutions and compile corresponding analysis software, but also has a broad application prospects.