Abstract: OBJECTIVE To analyze the syndrome differentiation rules of Ding Ganren's case records in external medicine. METHODS Association rules analysis on Ding's case records in external medicine was performed with modeling established by Apriori algorithm. Disease and syndrome differentiation characteristics of Ding's case records in external medicine was explored combined with conventional literature research and frequency statistics. RESULTS Cellulitis was a dominant disease in Ding's case records in external medicine， abscess， maxillary osteomyelitis and scrofula were also common. Compared with the syndrome differentiation in Chinese Traditional Surgery， Ding paid more attention to internal syndrome rather than identified the interior and exterior in the syndrome differentiation of cellulitis. Ding took exterior excess heat syndrome as the main syndrome of infectious swollen head rather than interior heat syndrome. In addition， the cases that were differentiated as blood deficiency and qi stagnation or yin deficiency and qi stagnation were more common than conventional external syndromes such as qi stagnation and blood stasis，phlegm and blood stasis binding and dual deficiency of qi and blood. CONCLUSION The differences of the common surgical diseases syndrome differentiation of Ding and Chinese Traditional Surgery reflect Ding's unique experience in exterior and interior syndrome differentiation. The coexistence of yin and blood deficiency and qi stagnation usually occurs in Ding's case records in external medicine such as tumor， cancer， scrofula and suppurative osteomyelitis， which reflects Ding's understanding about lesion mechanisms of "deficiency resulting in stagnation" and "stagnation resulting in deficiency". This enriches the TCM theory of relationship between qi and blood， expands the thinking of TCM syndrome differentiation in external medicine.