Abstract: Analysis is made on the cutter-orientation capability of using the 6-TPS parallel machine tool for surface machining. At first, the constraints-result from the cutter contact interferrence and cutter edge interference, the length limit of extensible struts, the subchain interference, the angle limit of joints, the singularity configuration of the machine-effecting on the cutter orientation are analyzed, and the equations expressing these constraints are acquired. Then, the effect of the setting of the same side joints on two adjacent subchains on the calculation of subchain interference test is investigated, and the formulas to determine the distance between the same side joints are derived aiming to reduce the calculation complexity. Based on the obtained equations, an efficient algorithm to calculate the allowable value region of the cutter-orientation angle for surface machining using the 6-TPS parallel machine tool with the flat cutter is presented. The algorithm can be used to control the orientation of the cutter so as to avoid over-cutting in surface machining.