Abstract: The pisolitic tuff, occurring in the Xinmin Formation in Ar Horqin Qi, Inner Mongolia, contains 65% of volcanic pisolites (or volcanic mud balls). The volcanic pisolites are developed in concentric layered rhythmic texture, some of which are filled with feldspar crystal fragments around the pisolites. By analyzing the characteristics of texture and component of crystal fragments, it is considered that the pisolitic tuff is evolved from the flowing hot volcanic ash with high-energy and high-density, accompanied with atmospheric precipitation during volcanic eruption.