Many papers have recently studied the characteristics of industrial clusters from the angle of informal institutions, and formed two main routes of research. One focuses on discussing the positive contributions of informal institutions to promote cooperation between companies and reduce transaction cost, and the other studies the conditions under which informal institutions work and demonstrates the limitation and dynamic change of it's function in the development of industrial clusters. The paper comprehensively reviews and compares the literature of two research routes, and thus points out the direction for the relative further research.