Shipbuilding is a representative engineering-to-order (ETO) industry that commences product design and manufacturing only after contract signing. It is difficult to accurately predict production schedule at the contract stage, and is this is extremely important because the design tends to be unique and the delivery date should be included in the contract given the paucity of information of the product. Although the intermediate products exhibit high similarity, design modification typically occurs even after the production has begun, and this increases the difficulty of accurate planning. Additionally, the production process incorporates labor-intensive assemblies and joining, and it inherently involves the uncertainties in process time and procedures. Thus, shipbuilding companies attempt to manage production plans via dividing them into hierarchical structures and tend to rely on empirical knowledge and data from production history. Recently, discrete event simulation (DES) is actively searched for the shipyard schedule management, which is successfully applied to mass production industries. However, it is not widely applied due to the inherent characteristics of shipbuilding industry. In order to solve the problem, we propose a layered discrete event system specification modeling method for a ship production scheduling system that provides a layer concept for mixed level of information. The aim involves integrating all production information. Each layer exhibits a level of usable information details. Furthermore, it is designed to facilitate cross-linked information between different layers. Thus, we define a mathematical formalism as an extended form of discrete event system specification and apply it to a production schedule model. The model is simpler and easier to implement because it reflects characteristics of shipbuilding production.