Traditional Chinese Medicine (TCM) is one of the oldest systems of medicine. More and more attention has been paid to TCM application, but the variable quality of clinical trials with TCM impedes its widespread acceptance. The Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) 2013 Statement has established guidelines for designing clinical trials to ensure that the trial results are accurate and reliable. However, there are difficulties when applying SPIRIT 2013 Statement to trials with TCM, due to the unique theory and the characteristic of TCM intervention. An Extension to the original SPIRIT was developed to ensure the quality of trial design with TCM. As Chinese herbal formulae, acupuncture and moxibustion are common and representative interventions in TCM practice, the executive working group determined that the SPIRIT-TCM Extension focus on these three interventions. Extension was developed through initiation, 3 rounds of Delphi consensus survey, and finalizing expert meeting. Seven items from the SPIRIT 2013 Statement were modified, namely, "title", "background and rationale", "objectives", "eligibility criteria", "interventions", "outcomes", and "data collection methods". The Extension includes the introduction of the concept of TCM pattern and 3 major TCM interventions, with examples and explanations. The SPIRIT-TCM Extension 2018 provides suggestion for investigators in designing high quality TCM clinical trials. It is expected that wide dissemination and application of this extension ensure continuous improvement of TCM trial quality throughout the world.