In this paper we present the Grid environment that supports application building basing on a High Level Architecture (HLA) component model. The proposed model is particularly suitable for distributed multiscale simulations. Original HLA partly supports interoperability and composability of simulation models, where connections between modules (federates) in a simulation system (federation) are defined and set by federates themselves. On the contrary, in the proposed component model the particular behavior of component and it’s connections are defined and set by an external module (e.g. builder) on the user request which is more flexible and increases reusability of components. We are also proposing to integrate our HLA component solution with the Grid which will allow users working on distributed simulations to more easily exchange the models already created. The focus of this paper is on design of the HLA component. We show how to insert simulation logic into a component and make possible to steer from outside its connections with other components. Its functionality is shown on the example of multiscale simulation of a stellar system.