Shrinkage formation often causes fatal defects in castings. Recently, the development of computer technology has realized effective methods for predicting shrinkage formation. Particle method is a Lagrangian method that uses points representing continuum body as calculation elements, and the points can move freely in space. This method can thus calculate flow and shrinkage formation directly and simultaneously. In this study, solidification simulation and flow simulation programs based on the particle method were combined considering the temperature-dependency of density, and the resultant program was applied to the flow and solidification problems of a cylindrical pure Al casting. First, the flow calculation stability for a gently placed fluid was investigated and an improved method “Multiple relaxation” was proposed. The flow of fluid during solidification is quite slow ; and the particle method has the fundamental difficulty of calculating slow flow phenomena, because of the co-located arrangement of the pressure and velocity of particles which induces unnatural oscillation of pressure and velocity. In addition, only the gravitational force was taken into account after the pouring finished ; the inertia and viscous force were assumed to be negligible. When the inertia and viscous force was not considered and “Multiple relaxation” was applied, the calculation stability improved significantly, and direct-integrated simulation from the pouring to the finish of solidification was possible. Gravity adjustment was also incorporated and it reduced the calculation time significantly without sacrificing the validity of the results.