Knoop indentation is a simple method to measure elastic modulus of fine ceramic samples with small size. However, due to the poor accuracy and comparability, this method has not been widely used for a long time. Here, the elastic modulus of six groups of ceramics, glass and standard block of Knoop hardness were measured by using Knoop indentation method. It is found that the elastic modulus in this work was consistent with that obtained by using pulse excitation and bending methods. However, due to the error transfer effect, when the indentation size b′/a′ was greater than 0.13, the relative deviation of the calculation results of H/E and E with Marshall formula would be 12 times greater than the size measurement error, resulting in unreliable results. Therefore, Knoop indentation method was suitable for measuring elastic modulus of brittle materials with small plastic deformation. When the vertex was not clear due to poor surface polishing or slight cracking of the indentation, the diagonal length could be calculated by collecting the point coordinates on the edge of the indentation, which could improve the measurement success rate under high loads.