This article deeply discusses the applicability of the sources of commercial customary law. Firstly

it explains the concept and characteristics of commercial customary law. Its concept covers a collection of unwritten behavioral rules in all levels and links of commercial activities. The characteristics include spontaneity originating from practice

universal applicability within a certain range

and flexible adaptability in the face of changes. Then

it explores its applicability from two aspects: international commercial intercourse and domestic commercial practice. Internationally

it can promote the smooth progress of trade

unify trading rules

and enhance transaction trust. It is also an important basis for resolving international commercial disputes. Domestically

it can fill the gaps in domestic laws in emerging fields and special industries

and also adapt to local commercial characteristics and needs. However

its applicability faces many challenges

such as the coordination problem with domestic laws

including legal conflicts and the establishment of coordination mechanisms; and challenges brought by modern business innovation

such as the application of new technologies and business model innovation. Finally

countermeasures are proposed

emphasizing the need to strengthen research and application

establish coordination mechanisms

and improve and innovate rules. Enterprises and legal practitioners also need to strengthen learning and understanding to give full play to the role of the sources of commercial customary law

promote the healthy development of business

and provide legal support for the prosperity of global business.