Postherpetic neuralgia （PHN） is a type of persistent and intractable nerve pain， which pertains to the category of collateral diseases in traditional Chinese medicine. Its disease location is consistent with that of collateral diseases， as is its course and the pathogenesis of various forms of pain. The key to the pathogenesis of PHN is the damaged but unrecovered collateral. Therefore， we differentiate three stages of PHN and treat respectively based on the collateral theory. The pathogenesis of the initial stage is toxin damaging the collateral， and the self-formulated Qingdu Shuluo Formula is prescribed to clear heat and remove toxin， smooth the collateral and relieve pain. The pathogenesis of the middle stage is blood stasis obstructing the collateral， and the self-formulated Huoxue Tongluo Formula is prescribed to activate blood circulation and relieve blood stasis， dredge the collateral and relieve pain. The pathogenesis of the advanced stage is collateral deficiency without recovery， and the self-formulated Buxu Huluo Formula is prescribed to benefit qi and nourish yin， protect the collateral and relieve pain. Meanwhile， medicinal pairs and channel-ushering medicinals are selected accordingly with the change of pain location and nature. If the topical pain is persistent and refractory， collateral-pricking and blood-letting should be used to remove stasis， generate new blood， activate the collateral and therefore improve the therapeutic effect.