The moisture content of coal seam roof has a major impact on the coal bed methane (CBM) exploitation. The No. 15 coal seam roof in Taiyuan Formation in southern Qinshui basin is mostly composed of limestone ( K2) which distributed continuously, and less and scattered mud. Limestone aquifers would affect the drainage of coal bed methane. From the aspects of limestone's thickness, the crack development, the coal seam and roof connection and the regional hydro-geological conditions,' this paper discussed the impact of limestone on the exploitation of coal bed methane. The results indicate that the water richness of the limestone is low, but is high in some places where the faults and karst collapse are developed. The thickness of limestone has nothing to do with the gas and water production of the CBM wells. The cracks of limestone are well developed, most of which are full of calcite, resulting in poor hydraulic conductivity and storage performance. There are two connection types between limestone and No. 15 coal seam. One is direct connection that limestone overlays No. 15 coal seam, the ojher is indirect connection that mud, sand and No. 14 coal seam are contained between limestone and No. 15 coal seam. The CBM wells have a much higher gas and water production in the directly contacted layers than in the indirectly contacted layers. And the lithology and thickness of the No. 15 coal seam roof do not affect the gas and water production.%煤层顶板的含水性对煤层气的开采有重要影响.沁水盆地南部上石炭统太原组15号煤层直接或间接顶板多为灰岩,其中以K2灰岩为主,连续分布.顶板泥岩较少,呈零散分布.灰岩的富水性对煤层气的排水降压有影响.因此,主要从灰岩的厚度展布、裂隙发育、与煤层的接触关系以及区域水文地质条件讨论其含水性对煤层气产能的影响.研究结果表明:(1)灰岩的含水性一般较弱,但当遇到断层或岩溶陷落柱较发育的部位,可能与其他含水层沟通,富水性较强.(2)15号煤层顶板灰岩的厚度与煤层气井的产水量并无直接关系,其裂隙较发育,但大多被方解石充填,导水和储水性能较差.(3)灰岩与15号煤层的接触关系有两种:一种是直接接触型,灰岩直接覆于15号煤层之上；另一种是间接接触型,灰岩与15号煤之间夹有泥岩、砂岩或14号煤层.直接接触型煤层气井的产水量、产气量比间接接触型高.间接接触型15号煤层直接顶板的岩性、厚度对产气、产水都没有太大影响.
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