The work aims to study the influences of impact velocity and configuration parameters on the in-plane cushioning properties of regularly-arranged circular honeycombs in the diagonal line. The finite element model of regularly-arranged circular honeycombs in the diagonal line was established with the software ANSYS/LS-DYNA. Based on this finite element model, the parametric simulations of the honeycombs with various configuration parameters and impact velocities were carried out. At different impact velocities in the diagonal line, the deformation modes, densification strains, plateau stresses and energy absorption properties were obtained and presented in tables and figures for the regularly-arranged circular honeycombs with different configuration parameters. At different impact velocities, the regularly-arranged circular honeycombs had different deformation modes in the diagonal line. At low or high impact velocities, the densification strain was only related to the ratio of cell wall thickness to radius, but was affected by both the impact velocities and the ratio of cell wall thickness to radius at moderate impact velocities. For a given ratio of cell wall thickness to radius, the in-plane plateau stress (or optimal energy absorption per unit volume) was linear with the square of impact velocity; at a given impact velocity, the in-plane plateau stress (or optimal energy absorption per unit volume) lied on the ratio of cell wall thickness to radius by a power exponential function. Based on the finite element results, the empirical formulas of densification strain, plateau stress, energy absorption per unit volume are derived.