Based on LI Gao's theory of "heavy obstruction" and "blockage of the nine orifices"， this paper proposes the pathological concept of "heavy obstruction and orifice blockage". It is suggested that the core pathogenesis of functional constipation （FC） lies in simultaneous sinking of spleen and lung， together with accumulation and obstruction of dampness and turbidity， resulting in impaired movement of intestinal qi. Within this framework， spleen deficiency with sinking of dampness is considered as the primary pathological mechanism of outlet obstructive constipation （OOC）， while sinking of lung qi is regarded as the key mechanism underlying slow transit constipation （STC）. When both pathological mechanisms coexist， mixed constipation （MC） develops. Guided by this theory， FC is classified into three patterns for syndrome-based treatment. OOC is treated by promoting bowel movement， descending turbid pathogens， and opening the orifices to restore function， with self-formulated Shengxian Tongqiao Decoction （升陷通窍汤）. STC is treated by diffusing lung qi， regulating spleen function， raising sinking qi， and promoting transportation， with self-formulated Xuanfei Yunpi Decoction （宣肺运脾汤）. MC is treated by regulating lung and spleen function， simultaneously raising clear qi and descending turbidity， with self-formulated Xuanyun Tongqiao Decoction （宣运通窍汤）. In clinical practice， modifications should be made according to accompanying syndromes and individual conditions.