With the higher integration density of wireless communication systems, the power density in a given volume is increasing, and the operating temperature is rising sharply, which directly affects the performance and reliability of the system. Thermal management has thus become one of the primary research topics. A three-dimensional thermal simulation model of the System-in-Package (SiP) is established to analyze temperature distribution and thermal resistance under natural and forced convection conditions. Then, a replacement verification scheme based on thermal test chiplets is proposed, enabling high-precision dynamic thermal monitoring and a thermal design optimization scheme is proposed. The results show that forced convection significantly reduces the junction temperature. The proposed methods provide valuable insights for future thermal management solutions in advanced electronic packaging.