Abstract：Painful diabetic peripheral neuropathy （PDPN） is clinically characterized by neuropathic pain，with a mostly protracted course that severely impairs patients' quality of life. In traditional Chinese medicine treatment， the syndrome differentiation is mostly conducted from the perspectives of collateral disease and blood stasis. Different from the traditional single-dimensional syndrome differentiation system， the author explores the overall pathogenesis and treatment methods of PDPN from the three-yin perspective of the three-yin and three-yang syndrome differentiation system in Shang Han Lun （Treatise on Cold Damage）. Combined with the theories of zang-fu organs， meridian and collateral， eight-principle syndrome differentiation， and chronic diseases transforming to collaterals， it is believed that in the early stage of the disease，the pathology locates in Taiyin，mainly manifested as dampness stagnation due to spleen deficiency and malnutrition of skin. As the disease progresses，it transmits to Shaoyin and Jueyin，triggering the pathological changes of cold congealing in meridians and intermingled cold and heat，which constitutes its main onset process. There are also cases where patients have congenital deficiency，and pathogenic factors directly attack Shaoyin and Jueyin across meridians， leading to severe conditions. In terms of treatment， the main principle is to warm and unblock the three yin meridians， conduct syndrome-differentiation along respective meridians， simultaneously give consideration to removing blood stasis and unblocking collaterals， and heavily employ insect-derived medicinals to search out and eliminate collateral pathogens.