In recent years, various types of applications of electromagnetic techniques to microwave thermal therapies have been developed. The authors have been studying the coaxial ring-slot antenna. We analyses the temperature distribution pattern and lesion size on hepatic cancer at frequency of 2.45GHz. We set the potential difference between the inner and outer conductors were 50V and set duration time for microwave ablation in the range 60s, 100s, 200s and 300s. From the simulation results of our previous studies, Numerical electromagnetic and thermal simulations are used to optimize the antenna design and predict heating patterns. Numerical results show the temperature distributions that all time had similar characteristics but, there are differently at the lesion size. When we set the ablation time was 300s the lesion size was larger, with a lesion width approximately 17 mm, compared to 10 mm for set the ablation time was 60s. If we considered the lesion volumes at the ablation time was 300s this case can be induced the highest temperature in cancer tissue and maximum ablation cancer tissue (3.74cm3). In addition, we also set the boundary conditions on temperature control mode which maximum temperature control within hepatic cancer at 96°C, duration time at 300s. From the simulation results, the volume of lesion size was 0.98 cm3, lesion width and depth approximately 11mm, 19mm. respectively.