[Purposes]Consider a nonlocal boundary value problems of a class of Riemann-Liouville fractional differential equations on infinite intervals. The nonlinear term of the equation are dependent on three lower-order fractional derivative terms, and the boundary value condition is the sum of fractional integral and multipoint boundary value conditions. [Methods]Firstly, the Green function of the corresponding boundary value problem is constructed, and some properties of it are obtained. Then, the existence and multiplicity of solutions to this boundary value problems are studied by using Leray-Schauder nonlinear alternative theorem, the relevant properties of Green function and monotone iterative method. [Findings]Two sufficient conditions that the boundary value problem has unbounded solution and two positive solutions are obtained respectively. [Conclusions]The applicability and feasibility of the main results are verified by examples, and some existing academic research results are extended.