The coming 5G communication system is giving great challenge to power amplifier (PA) since the increasing power density and highly integrated package demand. Based on this situation, this paper proposes a novel optimized design method, which combines the electric and thermal analysis result, to improve the reliability of power amplifier. The first step of this method is to design the circuit and layout of power amplifier. The subsequent step is to build an accurate model for thermal analysis based on the calculated parameters from circuit and layout. At last, utilizing the thermal distribution result of multi-heat sources inside chip optimizes the circuit and layout to reduce the working temperature and parameter error. By associating the electric design together with thermal result, the proposed method successfully overcomes the disadvantage of traditional temperature simulation methods which separate thermal analysis procedure from circuit design. In this paper, both circuit design and chip modeling are based on 4G LTE product parameters to verify the feasibility of proposed method. By analyses the temperature distribution of multiple on-chipheat sources and its influence on PA circuit performance, the experimental results confirm that through several circuit design and thermal simulation iterations of this method, the reliability of power amplifier chip can be optimized on the premise of minimizing area cost.