Based on our constructed robust π/2 mode converter, we report a concise yet high-efficient experiment to realize the detection of high-order orbital angular momentum (OAM). The π/2 mode converter that consists of a pair of cylindrical lens is actually not new. However, our experiment show clearly its excellent robustness, as we have detected the high-order OAM numbers up to ℓ = 150 carried by standard Laguerre-Gaussian (LG) modes. The observed patterns of two-dimensional optical lattices indicate that the radial index <i>p</i> of LG beams can be straightforwardly inferred as well. Our demonstration has potential in both classical and quantum information applications where high OAM modes are needed.