Many process parameters influence the properties of rigid PVC pipe. In this study, influence of CaCO3, thermal stabilizer as well as mixing temperature of the feed material and melting pressure of extrusion process; on thermal and mechanical properties of rigid polyvinyl chloride pipe were studied. Model design and result analysis was done using Design of Experiments. The mixture-process approach with D-optimal design was selected to plan the experimental set up. The result indicates that, increasing Calcium carbonate content significantly increases the densities of PVC composites. Tensile strength, elongation at break and flexural strength decrease significantly with CaCO3 content. The increment of both CaCO3 and thermal stabilizer improve vicate softening point (vicat hardness) and oven stability of the extrudate. But, Variation of mixing temperature and extrusion die melting pressure has not significant effect .Increasing mixing temperature increases tensile strength, % of elongation and flexural strength properties of extruded rigid PVC pipes. Finally, The results analysis showed that a minimum cost can be achieved through using 84.52% virgin PVC, 16.66 % CaCO3, 3.82% stabilizer and the material is mixed at mixing temperature of 120OC and extruded at melting pressure of 3mpa with an optimal response value of tensile strength of 50.28N/mm2, percentage of elongation 81.24%, flexural strength 89.39mpa, specific gravity 1.45, vicate softening point 83.59OC and % of change in length) -0807%).