Abstract: Based on the one-dimension two-phase drift flow model, the simulation of system characteristic under HTRL-5 condition was performed. The bifurcation characteristic of two-phase flow system under natural circulation condition was analyzed. The parameter effect on the bifurcation characteristic was also analyzed. The results show that the bifurcation phenomenon will occur under certain conditions and the bifurcation phenomenon will occur at the tangent point of the characteristic curve of the system. The bifurcation phenomenon will disappear while the system pressure increases or the heat flux decreases to some extent.