Lanshan is a mountainous county located in the east of
Jiuyi Mountains on the northern side of the middle
Nanling Range. The county is bordered to the southwest by
Jianghua County, to the northwest by
Ningyuan County, to the northeast by
Jiahe County, to the east by
Linwu County, to the southeast by
Lianzhou City of Guangdong. It covers , the county is north to south with west to east. Lanshan has a
humid subtropical monsoon climate with an annual average temperature of , annual rainfall of . There are 69 rivers with drainage area of more than 10 square kilometers or length of more than 5 kilometers, most rivers belong to the
Yangtze River system, less to the
Pearl River system. The county is the source place of the
Xiang River, originating from
Yegou Mountain () in
Zhulin Village () of
Xiangjiangyuan Town. ==Administrative divisions==