Objectives : In this study we investigated characteristics of eight extra meridians based on the chapter of Pyoung Gi Kyoung Pal Maek Byoung(PGKPMB) of the Pulse Classic(Maijing; PC) and the 27, 28, and $29^{th}$ question of the Classic of Difficult Issues(Nanjing; CDI). Methods : We searched out the contents of eight extra meridians in historical background, the principal and circulation of eight extra meridians, and the symptoms and pulse diagnosis of eight extra meridians on the PGKPMB of the PC and the 27, 28, and $29^{th}$ question of the CDI. Results and Conclusions : About development of eight extra meridians, content which was scattered in the CDI was supplemented and developed in the CDI. Also taking over the content in the CDI, the meaning of the eight extra meridians was expanded and supplemented in the PC. In the PC, the mechanism about symptom of eight extra meridians especially has been described. Also materialization of symptom which linked to pathogenic pulse of eight extra meridians had a great impact on future generation.