According to the situation of need of accurate micro-ohm measurement, a micro-ohmmeter system which based on four-line method is designed. This system adopts modularization design which includes power supply circuit, constant-current source, A/D converter and display with LCD. The accuracy of measurement is apparently improved because the adoption of four-line method, which effectively canceled the affect of lead resistance and contact resistance in low resistance measurements by separating the current input and the voltage-sensing leads. The high accuracy also results from the design of voltage follower in the voltage-measuring port, which made the current in voltage-sensing leads is zero. The experimental data indicate that the device can realize the resistance measurement within 1μΩ to 2MΩ automatically. Moreover, the tester has the function of resistance separation, which can be applied in resistor and electronics manufacturers for automated inspection.