Large-scale information systems must be populated with large-scale live data to ensure the testing & simulation effectiveness. The paper presents ISDGen, an integrated tool that supports automated simulation data generation for object-oriented software systems. It uses initiation analyzer to build statistical properties into software analysis/design models, which are then transformed into program code by its code generator; during system testing, its data generator can extract statistical information of software elements, and generate data to simulate system behavior automatically and accurately.