A novel method for aircraft conflict resolution in air traffic management (ATM) using physics informed deep reinforcement learning (RL) is proposed. The motivation is to integrate prior physics understanding and model in the learning algorithm to facilitate the optimal policy searching and to present human-explainable results for display and decision-making. First, the information of intruders’ quantity, speeds, heading angles, and positions are integrated into an image using the solution space diagram (SSD), which is used in the ATM for conflict detection and mitigation. The SSD serves as the prior physics knowledge from the ATM domain which is the input features for learning. A convolution neural network is used with the SSD images for the deep reinforcement learning. Next, an actor-critic network is constructed to learn conflict resolution policy. Several numerical examples are used to illustrate the proposed methodology. Both discrete and continuous RL are explored using the proposed concept of physics informed learning. A detailed comparison and discussion of the proposed algorithm and classical RL-based conflict resolution is given. The proposed approach is able to handle arbitrary number of intruders and also shows faster convergence behavior due to the encoded prior physics understanding. In addition, the learned optimal policy is also beneficial for proper display to support decision-making. Several major conclusions and future work are presented based on the current investigation.