In this study, finite element modeling of cross-scale high-speed transmission links on composite ceramic substrates is conducted. The cross-scale transmission link is composed of micro-bumps connecting the chip, a redistribution layer (RDL) and through ceramic vias (TCVs) on low temperature co-fired ceramic (LTCC), an RDL and TCVs on high temperature co-fired ceramic (HTCC), and finally, a termination at the ball grid array (BGA). A parametric scan analysis is performed on critical parameters influencing transmission performance, including the thickness and spacing of the RDL. Optimization designs are applied accordingly. The findings indicate that optimizing the thickness of the RDL can significantly improve transmission performance and ensure signal stability. Adjusting the spacing between RDLs reduces electromagnetic interference and crosstalk, further enhancing signal integrity. The simulation results show that reduced return loss is achieved in the optimized transmission link, while low insertion loss is maintained over the 10 MHz to 30 GHz frequency range. Improved noise margins and signal stability are revealed by time-domain eye diagrams, confirming enhanced transmission quality. Multi-port signal path simulations verify that strong crosstalk resistance and efficient signal transmission are demonstrated by the transmission link in high-density, multi-channel systems.