Abstract: This paper introduces some of the key algorithms of TranSpirit,which is a newly developed functional model extractor for full custom circuits. In the presence of secondary precharge and fork structures,the traditional paralle-l serial compression algorithm can not work well.To solve this problem, we propose a novel algorithm to analyze the dynamic circuits.Our algorithm for tristate gates can handle more complex structures.In addition,a more efficient algorithm for pass transistor logic is also presented. The experimental results show that TranSpirit can handle most of the circuits used in microprocessor design and has high extraction speed.