The collaborative design for a large-scale optical instrument is presented for fully considering the design process within an integrated framework, which mainly includes opto-mechanical structure CAD, CAE and the integrated information platform product data management (PDM). The whole design process is based on the virtual main model to realise parameter driving through model transformation and data sharing. The integrated frame of CAD/CAE/PDM is presented. Then the key aspects for a large-scale optical instrument, especially the advanced design by opto-CAD software tools and Zernike polynomial fit, are discussed. An application case is also provided, including optical design, structure design and analysis flow. The collaborative design method can well realise design optimisation with high efficiency.