In this paper, we obtain some results of finite determination for vector fields and 2-closed forms. (Finite determinated vector fields or forms admit polynomial models). The whole paper is based on a study of certain singular differential equations such that $X.f = h$ where $X$ is a singular vector field. The most important results concerning vector fields are obtained for germs in the plane. We give conditions under which formai equivalence or existence of format integral implie $C^{\infty}$-equivalence or existence of $G$ integral. For démonstrations, we use the "blowing up" method and some other results of F. Takens and F. Dumortier. We also study germs of 2-closed forms in $R^{4}$ and show that ail the germs of codimension less than 3 are stable.