Integrated Solar Combined Cycle (ISCC) system is considered as a promising route to utilize both solar energy and fossil fuel. However, due to the absence of a unified framework and universal analysis of ISCC, it is difficult to achieve direct performance comparison between different integrated system schemes under the unified evaluation system. In the present work, a generalized model of ISCC system was proposed and established, which covered various integration schemes of solar energy taken into the Brayton and the Rankine cycles and the different integrated systems were reasonably summarized. Based on the model, the unified expression of fuel-savability was derived. The expression was verified and applied to evaluate the lateral performance of different integration schemes. Secondly, based on the idea of energy grade coupling, the "allocation effect" in ISCC system integration was revealed by using the bridge term in the unified expression, that is, the proportion of the total input (exergy) allocated to the Brayton cycle and Rankine cycle changes due to the different positions of solar energy input. Thirdly, based on previous work, the "superposition effect" was expanded that the total system fuel-savability was comprehensively determined by the superposed sum of the basic term, which was the direct benefit of local solar integration, the floating term, which stood for the explicit influence of solar integration on each main component, and the bridging term, which stood for the implicit inter-cycle influence of solar integration. This work provides theoretical guidance for the research and application of more generalized multi-cycle systems integrated with solar energy.