Place the roasting pan in the oven and roast at a high temperature for half an hour. This will create a delicious crust around the leg of lamb. Roast for another hour at this lower temperature to make sure the meat gets cooked all the way through. Use a meat thermometer to check the internal temperature of the lamb and determine if it's ready. Leg of lamb tastes best when it's cooked between medium rare and medium well.  For medium rare leg of lamb, remove the dish from the oven when the internal temperature has reached between 145 and 150 degrees Fahrenheit. For medium or medium well leg of lamb, remove the dish from the oven when the internal temperature has reached between 150 and 155 degrees Fahrenheit. Tent aluminum foil over the baking dish and let the lamb rest. This gives the juices time to reabsorb into the meat, creating a succulent, tender dish. After 15 minutes, you may carve the lamb.

TL;DR in Chinese:
烤羊腿30分钟。 把温度降低到177摄氏度，继续烤。 将羊腿放置15分钟。