As microprocessor performance grows, high throughput and the power management are becoming more important on embedded real-time systems. Real- Time Voltage and Frequency Scaling (RT-VFS) has been proposed to reduce the power consumption and ensure real-time constraints. An imprecise computation model adds an optional part to Liu and Layland's model to improve the quality of computations. This paper proposes the scheme to integrate an imprecise computation model and RT-VFS that can reduce the power consumption and improve the quality of computations within real-time constraints. Moreover, we implement this scheme on Dependable Responsive Multithreaded Processor (D-RMTP). D-RMTP is a prioritized simultaneous multithreaded processor for embedded real-time systems and D-RMTP system in a package supports RT-VFS. We implement the proposed scheme by use of D-RMTP original features to improve the quality of computations and reduce the energy consumption. Through experimental evaluation, we show that the proposed scheme satisfies both the lower energy consumption and higher performance on real environments. In our evaluation, the proposed scheme achieves a maximum of 135% improvement of the quality of computations per energy consumption.