Abstract: Ooids are one of the common particles in coating grains in carbonate rock. The origin of ooids has been one of the most important scientific problems to which the geologists have paid close attention. It is very important to know and explain the sedimentary environment. There are multi-period stromatolitic biostromes or stromatolitic bioherms in the Cambrian strata at the Xiaweidian section in the western suburb of Beijing. The authors found that benthic ooids are largely developed in the top part of the Gushan Formation and the lower part of the Fengshan Formation. An analysis of their formation characteristics and microscopic fabric patterns shows that the origin of benthic ooids was closely related to microbial action, thus supporting the hypothesis of microbes to some extent. What is more, the discovery increases the diversity of the carbonate particles. On the basis of previous researches, the authors have traced the scientific meaning of this problem so as to provide some useful clues for thorough understanding of the form of microbial carbonate and microbial-mat.