The invention discloses a mechanical arm motion planning method based on deep reinforcement learning. The method comprises the following steps of 1, acquiring an environment image once before a mechanical arm moves, wherein the environment image comprises the mechanical arm in an initial state, a moving target point and an intermediate obstacle; 2, according to the acquired environment image, utilizing the target partitioning algorithm to separate a prohibited area, a working area and a target position from one another, and reconstructing a planning space; 3, dividing the reconstructed planning space into three-dimensional grid spaces, and establishing binarized grid spaces; 4, solving the corresponding analytical solution of each joint of the mechanical arm under known terminal coordinates by utilizing the robot inverse kinematics, and determining the relative positional relationships between the mechanical arm and the planned space boundary, the prohibited area boundary and the moving target under the global coordinate system; and 5, planning the motion strategy for the mechanical arm and acquiring the optimal motion strategy, so that the mechanical arm moves to the target position at the minimum cost under the premise of avoiding the obstacle.