Due to the fact that effective rational approximation of fractional operator was necessary in practical application, the rational approximation of 1/2(n) order fractional operator was constructed. To take the approximation as the transfer function, the circuit of 1/2(n) order fractance, which intended to test the performance of the approximation algorithm, was designed and realized through RC elements. A fractional control system made up of the fractance was given. Bode diagram and Nichols diagram illustrated its frequency character, while its time domain character and initial value problem were illustrated by state equation of the system. The effectiveness and good performance of the proposed method has been proved through the calculation example both in frequency and time domain.