S.G. Kazantsev Orthogonal polynomial basis in the space of vector functions ${\bf H}_0^1$ and Stokes system in a ball Abstract. In the homogeneous Sobolev space of vector functions ${\bf H}_0^1({\mathbb B}^3)$ orthogonal polynomial basis is constructed. Some of this vector functions, in particular, are vector potentials for solenoidal fields from the basis of the space $ {\bf L}_2({\mathbb B}^3)$. As the result, the Dirichlet boundary value problem for the stationary Stokes system in a ball is solved. The solution is presented as a series on the constructed polynomial basis vector functions. Keywords: Vector spherical harmonics, vector functions, potential field, solenoidal field, polynomial vector functions, Sobolev space, orthogonal basis,Stokes problem