Under applied loadings, particle aggregate produces complex effect of contact force chain between particles. In order to elaborate the formation and development of force chains and to describe the distribution and configuration of the force chains，based on the principle of optical stripes in photoelastic material under loading, an experimental equipment is developed that performs photoelastic test on particle aggregates under biaxially loading and bilaterally flowing conditions. Through case studies for different combinations of loading and particle flow conditions, the effect of force chain of particle aggregates in variety of form and distribution has been generally recognized. After the flowing of particle aggregates, an arch structure forms upon the flowing gate, which can support the upper particle aggregates to maintain the stability of the upper structure. The presented work provides a fundamental experiment method for studying force chain structure of particle flow and mesomechanical behavior of particle aggregates under different backgrounds, particularly, the special design which allows particles to flow out from both the bottom and side gates provides convenience for the practical application.