Understanding and optimizing the power consumption of smartphones has become an important research topic. It is necessary to have a dynamic power estimation tool for hardware and software developers so that they can develop energy-efficient applications and construct energy-efficient smartphone systems. Previous work has proposed various power models for estimating the power consumption. However, these models lack granularity and accuracy. In this paper, a power model for smartphones considering hardware utilization and power delay is proposed. The model makes each hardware component more fine-grained and includes the power delay. Therefore, it can more accurately estimate the real-time power consumption. The model is based on a nonlinear regression structure. First, the model is determined by making each system variable modular from the target device. Then, the specified model is identified by test cases and the final coefficients concerning the power consumption are confirmed. Finally, the estimated power is compared with the actual power measured. Experimental results demonstrate that the average absolute error of power model is less than 4.6% in common scenarios, which obviously improves the accuracy of evaluation.