This paper investigates recent progress on a-posteriori error analysis for the high-order finite element method(FEM). The paper will discuss the differences between a-posteriori error estimations for lower-order FEM and those for high-order FEM, and analyzes the technical and methodological differences on a-posteriori error estimations for high-order FEM in one dimension and in high dimensions. Based on a newly established mathematical framework of the Jacobi-weighted spaces, a-posterior error estimators and indicators for the p-and h-p version of FEM are proposed, and its prospective is discussed.