A system for determining a state of a power relay assembly includes: a power relay assembly for determining electrical connection states of first and second input-output ports; a relay controller outputting a control signal; a battery management system for determining a connection state of the relay and directing a connection state adjustment of the relay; and a voltage sensor for sensing a voltage of the first input-output port and outputting a state signal. By determining the state of the power relay assembly, it is possible to take quick action against trouble by subdividing and distinguishing a type of abnormality of the power relay assembly, and to prevent a larger problem from occurring by diagnosing relay abnormality in advance and quickly taking a fail safe operation.