A parametric design problem of the finite time obse rvers for the linear time-invariant systems and som e important properties of finite time observers are investigate d in this paper. Based on the parametric solutions for a class of Sylvester matrix equations, the parametric expressi ons of all the gain matrices for the finite time ob servers are proposed. Based on the above design results of fini te time observers, the corresponding transfer prope rty and separate principle for the finite time observers ar e proved, respectively. Finally, a numerical exampl e shows the effectiveness of the proposed design method, the tr ansfer property and the separate principle of the p arametric finite time observers in the linear time-invariant systems .