Particle impacting on a liquid surface is frequently observed in natural and industrial processes. This study numerically investigates the critical sinking behaviour after the impact of hydrophobic micron particles on liquid surfaces. The effects of contact angle theta, density ratio D, and the Reynolds number Re on the motions of the particle and TPCL are analyzed. The dimensionless penetration depth of the particle increases with increasing theta and D, whereas the effect of Re is negligible. The relationship between the TPCL position on the particles and the normalised particle displacement is only determined by theta and almost unaffected by Re and D. For the critical sinking of hydrophobic micron particles, both fluid force and surface tension play important roles in the conversion of particle kinetic energy. A dimensionless energy conservation equation is constructed, based on which a simple criterion of critical sinking is proposed. The expression of this criterion is obtained based on the semi-empirical expressions describing the relationships of each dimensionless accumulated work with Re, theta, and D obtained from simulation results. Compared with existing criteria, the proposed criterion is more accurate because it considers the fluid force, TPCL movement, and other factors reasonably. (C) 2019 Elsevier Ltd. All rights reserved.