Abstract: Collaborative CAD aims to break through limitations of geographically distributed orgnizations and designers that use heterogenous legend CAD systems for products development, which can reduce time-to-market for new products. Replicated architecture is currently a hot research topic for constructing a collaborative CAD system due to the light network load, fast response and easy adaptation to heterogenous legend CAD systems. For replicated instant collaborative CAD system, more factors than traditional distributed and parallel computing should be taken into consideration. Instant collaborative parametric design, which is still an open challenge in the research community of collaborative design, must be realized before practical applications can be made. This paper proposes a scheme for parametric design in replicated instant collaborative CAD systems. This scheme concerns on several key factors which are optimistic concurrency control strategy, parametric collaborative design commands representation, parametric collaborative persistent naming, collaboration awareness. The proposed scheme has been implemented in our prototype system and works well.