In this study, a fluid flow and solidification simulation programs based on Moving Particle Semi-implicit (MPS) method, one of Lagrangian meshless method, were developed to achieve seamless simulation of casting processes. Multiple relaxations and biased velocity correction methods were proposed and introduced to a fluid flow simulation to suppress disordered movement and bounding behavior of particles caused by original MPS algorithm. The fluid flow simulation program was applied to the well-known benchmark lid-driven flow problems, and obtained results show that the proposed algorithms have high accuracy in spite of its low-resolution particle numbers. Heat transfer simulation program based on the MPS method was also developed, and interfacial heat resistance was considered in the program. The fluid flow and the solidification simulation programs were merged, and density change with temperature was introduced into the algorithm. Finally, casting process simulations from mold filling to solidification were carried out seamlessly with the proposed algorithms. As a result, generation of outer and inner shrinkage is shown, and predicted shapes of internal and external shrinkages agree well with experimental results.