This article explores some requirements for applying qualitative simulation algorithms to system dynamics models. The field of qualitative simulation lacks a specific procedure for modeling systems (subjects of its models are generally physical systems). Bringing together qualitative simulation techniques and system dynamics modeling techniques could benefit both fields. The structural correctness of system dynamics models is defined using constraint theory. An attempt is made to alleviate some problems of qualitative simulation algorithms by drawing upon system dynamics modeling methods and by establishing the structure for the propagation of constraints in these models.