A method for controlling operation of a hydraulic idle stop and go (ISG) system using an electro hydraulic power steering (EHPS) system includes measuring a pressure in an accumulator, a steering angle, and a steering angular velocity; determining whether the measured pressure in the accumulator is less than an absolute value of a first reference pressure; determining whether the measured steering angle is less than an absolute value of a reference angle when the measured pressure in the accumulator is less than the absolute value of the first reference pressure; determining whether the measured steering angular velocity is less than an absolute value of a reference angular velocity when the measured steering angle is less than the absolute value of the reference angle; and opening a solenoid valve when the measured steering angular velocity is less than the absolute value of the reference angular velocity.