In order to quickly get the positioning error value of the positioning parts in the machine tool fixture design, and provide the parameter reference for the improvement and design of the fixture, in view of the shortcomings of traditional positioning error algorithm, a dimension chain tolerance method was proposed to calculate the positioning error of the parts. Beginning from the establishment of the dimension chain model of the positioning error of the parts, the search of the composition rings in the dimension chain and the calculation of the closed rings, the solution of three kinds of positioning, including the outer circle, the inner hole and the plane of the parts was discussed by using the dimension chain algorithm of part positioning error, and the result was verified by using traditional method of part positioning error. The result shows that the dimension chain tolerance algorithm of part positioning error does not need to analyze and calculate the benchmark misalignment error and datum displacement error separately, and it is not necessary to determine the direction of error change, so that the calculation becomes simple and quick.