Assembling of a few particles into a cluster commonly occurs in many systems.How-ever,it is still challenging to precisely con-trol particle assembling,due to the vari-ous amorphous structures induced by ther-mal fluctuations during cluster formation.Although these structures may have very different degrees of aggregation,a quanti-tative method is lacking to describe them,and how these structures evolve remains un-clear.Therefore a significant step towards precise control of particle self-assembly is to describe and analyze various aggregation structures during cluster formation quantitatively.In this work,we are motivated to propose a method to directly count and quantitatively compare different aggregated structures.We also present several case studies to evaluate how the aggregated structures during cluster formation are affected by external controlling factors,e.g.,different interaction ranges,interaction strengths,or anisotropy of attraction.