针对口孜东矿121302工作面使用的四柱支撑掩护式液压支架适应性较差的问题，统计分析了121302工作面的矿压和支架受力特点，基于平面杆系建立了四柱支撑掩护式支架的力学模型，推导出支架极限外载荷大小和分布区间的解析表达式，得出支架外载荷与顶梁合力和底座合力是一一对应关系，支架能够平衡的外载荷必须满足其对应的顶梁合力和底座合力均在其长度范围内，否则，支架将不能保持稳定状态;支架极限外载荷区间不是完全覆盖顶梁长度，依据前后排立柱的最大工作阻力和最大拉力分为5个区域:前排立柱达到最大拉力区、后排立柱达到最大工作阻力区、前排立柱达到最大工作阻力区、后排立柱达到最大拉力区、无承载能力区，其中，无承载能力区的区间取决于支架高度、摩擦因数以及顶梁前端至底座前端的水平距离。通过实例分析了支架前后排立柱不同工作阻力分配比例和摩擦因数对支架适应性的影响，结果表明:支架前后排立柱工作阻力不能相差太大，太大会降低支架的适应性;顶底板松软和较大俯采角度的工作面，支架前后排立柱工作阻力分配比例6∶4时最为合理;通过增大中缸环形面积以提高后柱的受拉能力来提高支架适应性，为了保护导向套和立柱连接件不受损坏，立柱的上腔加装安全阀，并加强后排立柱的连接件强度;摩擦因数取负时，支架极限外载荷区间最小，随支架高度降低，支架极限外载荷区间增大;摩擦因数取非负时，摩擦因数越大，支架前端的承载能力越大，随支架高度降低，支架极限外载荷区间减小。

In order to overcome problem of poor adaptability for the four-leg chock shield hydraulic support used in the 121302 working face of the Kouzidong Coal Mine in China,the stress of the mine pressure and hydraulic support of 121302 working face are statistically analyzed. The mechanical model of the four-leg chock shield hydraulic support is established based on the plane bar system,and the analytical expression of the magnitude and distribution range of the ultimate external load of the hydraulic support is derived. It is concluded that the external load of the hydraulic support is one-to-one corresponding to the resultant force of canopy and base,the external load that the hydraulic support can balance must meet the corresponding resultant force of canopy and base within its length range,otherwise,the support will not remain stable. The ultimate external load distribution range of the hydraulic support does not completely cover the length of the canopy,according to the maximum working resistance and maximum tension of the front and rear legs,it is divided into five:the range where the front leg reaches the maximum tension,the range where the rear leg reaches the maximum working resistance,the range where the front leg reaches the maximum working resistance,the range where the rear leg reaches the maximum tension,and the range without bearing capacity. The distribution of the range without bearing capacity depends on the hydraulic support height,friction coefficient and the horizontal distance from the front of the canopy to the front of the base. The influence of different working resistance distribution ratio and friction coefficient on the adaptability of the hydraulic support is analyzed through an example,the results show that the working resistance of the front and rear legs of the hydraulic support should not be too different,which will reduce the adaptability of the hydraulic support. If the roof and bottom of the working face are soft and there is a large angle of mining,it is most reasonable when the ratio of working resistance of the front and rear legs of the hydraulic support is 6 ∶ 4. The adaptability of the hydraulic support is improved by increasing the annular area of the second-cylinder of leg to improve the tensile strength of the rear leg. In order to protect the guide sleeve and the leg connector from damage, the upper cavity of the leg is equipped with a safety valve,and the strength of the connector of the rear leg is strength- ened. When the friction coefficient is negative,the ultimate external load range of the hydraulic support is the smallest, the ultimate external load range increases with the decrease of hydraulic support height. When the friction coefficient is non-negative,the larger the friction coefficient is,the larger the bearing capacity of the front of the hydraulic support is,the ultimate external load range decreases with the decrease of hydraulic support height.