The accuracy of Fused Deposition Modelling (FDM) manufacturing process can be affected by a lot of factors. Thus this study proposes in-situ dimensional accuracy optimization to study the effect of each factor and find the optimum set of print parameters. The research focuses on refining 3D printing accuracy and overcoming the difficulties on access to the internal structure and external structure. The study addresses current limitation in 3D printing precision caused by complexity of the model that being printed with the aids of image processing method. This includes implementing of image processing through a camera system to capture layered image to access to internal structure and external structure and improving the accuracy of the 3D printing. Based on the result, the optimal parameter of model is the infill density of 20%, printing speed of 40 mm/s, and nozzle temperature of 210 ℃.