Abstract: The rock breaking of the abrasive gas jet is determined by the abrasive acceleration effect, and the spatial and temporal characteristics of the air flow field are the most important factors in determining the distribution and acceleration of the abrasive. The pressure ratio β (the ratio of jet pressure to ambient pressure) affects the spatial structure of the air flow field and the pulsation frequency. Therefore, the temporal and spatial evolution of supersonic air jet flow field was studied based on the β. To study the spatial and temporal characteristics of the flow field, the Schlieren experiment was used to obtain the grayscale photos of the air flow field, the flow field density was calculated by establishing the conversion model between the grayscale value and the density value, and then the spatial structure of the flow field was obtained. The pulsation frequency of the flow field was obtained by converting the time domain and frequency domain of the grayscale photos. The results show that the β can significantly affect the spatial structure and pulsation intensity of the flow field. When the β=1, the air jet is in a fully expanded state, and there is no obvious wave node structure in the potential core of the flow field. The flow density changes gently, and the pulsation frequency is concentrated at 100 Hz. As the β increases to 1.12, the supersonic flow appears slight expansion and compression, and the flow density changes more rapidly along the axial direction of the jet. The potential core presents obvious nodal structure, and the length of potential core is longer. Meanwhile, the flow field pulsates strongly and multiple pulsating main frequencies exist simultaneously. When the β continues to increase to 2, the airflow density along the jet axis shows a sharp increase, a sharp drop, the length of potential core decreases rapidly. However, the pulsation of the flow field is suppressed and the pulsation frequency decreases rapidly. With the further increase of β, after the airflow is out of the nozzle, its density will quickly decay to the ambient density value, the flow field oscillatory weakens, the pulsation frequency is again stabilized at 100 Hz.