An evaluating method by combination of particle swarm optimization and quasi-random sequence was proposed to detect precisely and evaluate the profile errors of freeform surfaces inspected by Computer Aided Design (CAD) model-directed measuring. In order to solve the un-repetitive problem between design coordinate system and measurement coordinate system when a Coordinate Measurement Machine (CMM) was used to inspect free form surfaces, Quasi Particle Swarm Optimization(QPSO)was proposed to realize the precise localization between measured surface and design surface. Then, according to the features of freeform surface form, the peak-valley error and root mean square error were used to evaluate the freeform surface forms together. The computation method of the objective function was described,in which QPSO is used to match the measured surface and the design surface and the detailed steps were established for solving parameter vectors by using QPSO. Finally, by calculating the surface profile errors of simulation example and many practical measured parts, the results verify that the proposed method can locate precisely freeform surfaces and the evaluation precision of freeform surface profile errors by the proposed method is higher 8%-15% than that by CMM software. The method is suitable for the form error evaluation of high precise freeform surface parts.