In software design, the reuse issue brings the increasing of web services, components and others techniques. These techniques allow reusing code associated to technical aspect (as software component). With the development of business components which can integrate technical aspect with HCI, the composition issue has appeared. Our previous work concerned the GUI composition based on an UIDL as UsiXML. With the generalization of Multimodal User Interfaces (MUI), MUI composition principles have to be studied. This paper aims at extend existing basic composition principles in order to treat multimodal interfaces. The same principle as in the previous work, based on the tree algebra, can be used in another level (AUI) of the UsiXML framework to support the Multimodal User Interfaces composing. This paper presents a case study on the food ordering system based on multimodal (coupling GUI and MUI). A conclusion and the future works in the HCI domain are presented.