Ship launching is an important step in the whole process of ship construction. In modern shipbuilding industry, longitudinal gravity launching method is suitable for most kinds of ships, and is still widely used in many shipyards. Exactly calculation of the ship’s floating state and force acting on the hull and sliders is very important for security of launching ships. The present paper investigated the floating state and hydrostatic force and moment acting on a multi-purpose cargo ship based on some useful data such as Bonjean curves, distribution of ship mass, coefficients of ship form and arrangement of slipway. The variations of buoyancy and draughts at bow and stern with slipping distance are calculated and compared for two cases.