Smart meters, one of the critical end-components of the smart grid, their related communications with other devices are facing more and more security challenges. Based on the practical application environment of the smart meters, this paper proposes a novel design framework of elliptic curve cryptosystem (ECC) suitable for smart meter applications. This cryptosystem is designed based on the low complexity polynomial multiplication, which has the features such as low resource usage and fast computation. To obtain the best operational performance of the cryptosystem, this paper firstly proposes architectural innovation on the polynomial multiplication and addition at the lowest level. Then, this paper also has optimized and updated the sequence of the point computation process at the highest level of ECC. Finally, this paper also presented a new implementation structure for ECC. The detailed experimental results on the field-programmable gate array (FPGA) device show that, compared with the existing designs, the proposed design has features such as small resource usage and fast computation time. In conclusion, the overall area-time complexity of the proposed design is at least 18.2% smaller than the existing results. The experimental results have also verified the feasibility and practicality of this cryptosystem in the smart meters. The proposed cryptosystem is suitable for smart meter systems in smart grid and it is worthy to popularize the proposed design.