我国煤储层渗透率普遍较低，如何提高煤储层渗透率是煤层气开发的重点和难点。近年来液氮致裂增渗煤体技术作为一种无水致裂增渗技术受到广泛关注。为揭示液氮冻结和冻融循环对煤体力学特性的影响，采用红外热成像技术对液氮冻结后煤样的温度分布特征进行研究，并对液氮冻结和冻融循环后的煤样进行单轴压缩和声发射测试，对比分析了液氮冻结和冻融循环前后煤样的波速、孔隙率、声发射和能量演化特征，并对液氮冻结煤体损伤作用机理进行了讨论。结果显示：① 经过360 min和12次冻融循环后，煤样的波速分别下降了58.2%和64.7%，波速在最初的冻结和冻融循环阶段中下降并不明显，随着冻结时间和冻融循环次数增加，波速逐渐下降。②随着冻结时间的增加，煤样的温度逐渐下降，液氮冻结180 s后，煤样的表面温度下降至−60 °C以下，由于煤颗粒的热传导系数不同，导致煤样中心处的温度呈波动分布。③液氮冻结和冻融循环后，煤样的弹性模量呈指数函数降低的趋势，而煤样的孔隙率则逐渐增加，液氮冻融后煤样的孔隙率增量大于液氮冻结后煤样的孔隙率增量。④单轴加载过程中煤样的声发射活动分为发展阶段、活跃阶段和剧烈阶段，煤样的最大声发射振铃计数和累积声发射振铃计数随着冻结时间和冻融循环次数的增加而减小。⑤液氮冻结和冻融循环会削弱煤样的储能极限，造成在单轴加载过程中峰值点处的总能量、弹性能和耗散能的减少。

The permeability of coal reservoir is generally low in China, how to effectively improve the permeability of coal reservoir is a key and difficult point of coalbed methane exploitation, Liquid nitrogen fracturing technology as a kind waterless fracturing technology has received extensive attention in recent years. In order to reveal the influence of liquid nitrogen freezing and freeze-thaw on the mechanical properties of coal, the temperature distribution of coal samples was monitored by infrared thermal imaging technology, and uniaxial compression and acoustic emission tests were performed on the coal samples after the liquid nitrogen freezing and freezethaw, the P-wave velocity, porosity, acoustic emission and energy evolution characteristics of coal samples before and after the freezing and freeze thaw were analyzed. The research result showed that: ①After 360 min freezing and 12 freeze-thaw cycles, the P-wave velocity of coal samples decreased by 58.2% and 64.7%, respectively. The P-wave velocity does not decrease significantly during the initial freezing and freeze-thaw cycle stages, the velocity gradually decreases with the increase of freezing time and freeze-thaw cycles. ②The temperature of the coal sample gradually decreases with increase of freezing times. The surface temperature of the coal sample drops below -60°C after the liquid nitrogen frozen for 180s, the temperature distribution fluctuations at the center of the coal sample occurs due to the different thermal conduction coefficient of the coal particles. ③After liquid nitrogen freezing and freezethaw, the elastic modulus of coal sample decreases exponentially, while the porosity gradually increases. The increase in porosity of the coal sample after liquid nitrogen freeze-thaw is greater than that after liquid nitrogen freezing. ④The acoustic emission activity of coal samples during uniaxial loading is divided into development phase, active phase and severe phase, the maximum acoustic emission ringing count and cumulative acoustic emission ringing count of coal samples increase with the increase of freezing time and freeze-thaw cycles. ⑤Liquid nitrogen freezing and freeze-thaw will weaken the energy storage limit of coal sample, resulting in the reduction of the total energy, elastic energy and dissipated energy at the peak point during the uniaxial loading process.