Aiming at the problems of attribution on measurement of the roundness-error for macro-axis, a new technology on the measurement of the roundness-error for macro-axis with combination of inductance micrometer and computer is introduced. Adopting the least square circle, gathering the parameter date of the surface profile of measured parts by using the inductance micrometer, testing and dealing with the parameter date with the SFKSWS made by ourselves. It is testified by theoretical analysis and experiments that the measurement system has many advantages, such as advanced technique, high-test precision, reliable performance, convenient operation and measurement online. The practical problem of the error-measurement for macro-axis online is solved by using the method.