in recent years, mobile phone sensing applications has been regarded as new paradigm to obtain ubiquitous environment data. Research on motivating smart phone users to participate in mobile sensing contributing their resources and maximizing the profit of platform is in full swing. Unfortunately, the location-based optimal task assignment problem in mobile sensing is an NP-hard problem. We transform the problem to the maximum weight independent set problem (MWIS) and proposed a polynomial-time approximation scheme (PTAS) to approximate this problem in the intersection graph models. We conducted the simulation experiment and it turns out that the practical performance of the proposed near optimal task assignment algorithm corroborates the theoretical analysis.