The invention relates to a stroke-measuring method for movable hydraulic cylinders of an artificial diamond synthetic compressor. A special measuring tool is adopted to accurately measure a gap between a top hammer of a movable hydraulic cylinder and a diamond synthetic block and sequentially adjust preset positions of the top hammer of the movable hydraulic cylinder, wherein the adjustment of movable hydraulic cylinder strokes means that three movable hydraulic cylinders in a natural state are simultaneously adjusted. The measuring method can effectively improve the stroke-measuring accuracyof the movable hydraulic cylinders, thereby ensuring the evenness of pressing six sides of the diamond synthetic block in the synthetic pressing process and greatly improving the stroke-adjusting efficiency of the movable hydraulic cylinders of the compressor. The method has simple and convenient operation, low labor intensity and strong reliability and can improve the synthetic quality of artificial diamonds.