Multiple array 3D sonic digitizer system is a product made for measuring the geometric structure of an arbitrary object in three dimension. This paper gives a theoretical performance evaluation of the system. The Cramer-Rao Lower Bound of the parameter estimates of a linear segment is derived. In addition, the distortion effect caused by the time-delay bias, including rescaling, rotation and bending of the original object, is clarified. A simple method using a line segment is proposed to calibrate the bias term arised in the different parts of the system. Finally a simulation gives a numerical demonstration of the previous analysis and performance improvement of the suggested method.