||Product geometry measurement is a critical step in the product development cycle. It provides dimensional and tolerance verification between mechanical design and measurement assuring the quality of the product. Traditional measuring strategy is based on experience rather than using a systematic approach. In this research, a Computer Aided Measurement algorithm for quality measurement of mechanical part is presented. It involves establishing a measurement datum, two dimensional measurement process planning and measuring strategy of a freeform surface. The vector-based datum transformation scheme is a standardized method to define the measurement datum to improve the quality of mechanical parts. Refer to mate condition of assembly model to identify the dimension and tolerance relation between a geometric feature and the measuring datum. Through Assembly Mating Map and tolerance analysis, a common measuring datum is defined to improve a measurement strategy with the same measuring vector of assembly features. The 'Vector Based Tolerance Differential Variation Algorithm' is a part of computer aided measurement to improve the quality of measurement process. It provides a systematic approach to establish the measurement process planning, minimizing the thermal effect for single plane measurement of regular features. This algorithm is based on positioning and geometric dimensional tolerance to establish the measurement sequence for single plane geometric measurement. The 'Segment Based Freeform Surface Measurement Algorithm' is an important geometric data linkage from product design (CAD) to 3D measurement for a freeform object. The measuring process plan of the proposed algorithm considers the machining condition (tool life) and curvature change of the measured surface to establish the optimized solution to generate the sampling points for CMM measurement programming, to save the measuring time and improve the quality control of the final product.