Pick out the woody bits of stem and separate the tender leaves and chop the parsley into 1/4" pieces. Then, blanch the parsley in boiling water for 20 to 30 seconds. Arrange the blanched parsley across the tray. Try to keep it flat and evenly spaced, with no big clumps of parsley sticking together. Turn the oven on to the lowest possible setting. The best time to do this method is after the oven has been turned off, following other baking. Otherwise, always err on the side of taking longer than having it too warm and burning the parsley. The exact time will vary based on the relative humidity in your area and the altitude. Keep an eye on it, because it might dry more quickly. It's ready when it crumbles easily in your fingers. Crush the parsley with your hands or in a mortar and pestle. Remove any remaining stalks. Store in a dry, dark place, or even the freezer. Parsley dried this way can be good for long periods of time, but will start to lose its flavor after several months.

TL;DR in Chinese:
用冷水把新鲜欧芹洗干净。 把牛皮纸铺在烤盘里面。 放在烤箱里。 用2到4小时烘干欧芹。 从烤箱里拿出来。 把烘干捣碎的欧芹放在一个贮存容器里。