The invention provides an input-series-output-parallel (ISOP) system having natural voltage sharing characteristic and a control method thereof. The system comprises n sub-modules, wherein each sub-module comprises a Boost converter and an LLC resonant converter, n is a natural number larger than or equal to 2, in each sub-module, the Boost converter is a front stage, the LLC resonant converter isa rear stage, an output of the Boost converter is used as an input of the LLC resonant converter, the two converters are connected by an intermediate bus capacitor, input ends of the Boost convertersof the n sub-modules are sequentially connected in series, a positive electrode of an input voltage source is connected with an input positive end of a first Boost converter, a negative electrode ofthe input voltage source is connected with an input negative end of an n(th) Boost converter, and output ends of the LLC resonant converters of the n sub-modules are connected in parallel and are respectively connected with a positive end and a negative end of an output resistor. By the system, no extra measure is needed to be added, input voltage sharing and output current sharing of the ISOP system can be achieved, and the influence of inconsistent parameter among the modules on a voltage sharing and current sharing effect is relatively small. The implement method is simple, and the reliability of the system can be greatly improved.