The invention provides a 7-ADCA crystal and a preparation method thereof. The X-ray powder diffraction pattern of the 7-ADCA crystal is shown in Figure 1. The preparation method comprises the following steps: adding 7-ADCA into water, adding alkali solution into the water, and regulating pH to be dissolved; adding alcohol into the solution and forming liquid to be crystallized of an alcohol/watermixed system; adding acid into the liquid to be crystallized, regulating pH till to be precipitated, continuously adding acid till pH is equal to 3.8-4.0, carrying out solid-liquid separation, washingand drying the obtained solid and obtaining the 7-ADCA crystal. The novel 7-ADCA crystal is prepared and obtained in the alcohol/water mixed solvent system, and is easily dissolved in a dichloromethane/tetramethyl guanidine system, so that the dissolving property of the 7-ADCA is greatly improved; by adoption of the 7-ADCA crystal as the raw material, the benefit for obtaining cephalosporin antibiotics with higher quality and the industrial application prospect is wide.