Objectives  In order to judge whether there is a falling deep situation on submarine,

  Methods  a underwater motion model of submarine is established, and the motion accuracy of the model is verified by experimental data; the falling deep of submarine is simulated and the motion characteristics are analyzed; the assumption that there is a critical static load at different navigation speeds is put forward, and the assumption is verified by calculation. The method of judging falling deep of submarine is studied, and the depth rate ∂H/∂t and pitch change rate ∂θ/∂t are used as the criteria for danger of falling deep of submarine.

  Results  It can quickly and effectively judge whether the submarine is in danger of falling deep.

  Conclusions  It has certain reference value for safe operation of submarine.