This paper summarizes and reviews the freehand 3D ultrasound probe calibration techniques based on the optical tracking system. It firstly introduces the current researches on existing calibration methods and divides them into point phantom, line phantom, plane phantom, and method without phantom based on their principles. Then two approaches are introduced for determining the calibration matrix, including the iterative and the closed-form methods. Next two types of indexes for evaluating the precision and accuracy of a calibration transformation are introduced. At last the characteristics of various calibration methods are analyzed from perspectives of precision, accuracy, time, reliability, scope of application, and ease of use. The existing problems and trends of the freehand 3D ultrasound probe calibration are also discussed.