The mass loss rate and the relative dynamic elastic modulus of concrete specimens were studied under varying fiber types,temperature and holding time in this work. Studied compressive strength and splitting tensile strength of series of samples which treated under different conditions. Influences of high temperature, holding time and fiber types for the primary physical and mechanical properties of concrete were discussed respectively. The improvement mechanism of organic fiber on the performance of concrete after high temperature was also investigated. The results revealed that, the mechanical performance of plain concrete was declined heavily after high temperature, even burst after temperature ar-rived 700℃to 800℃. Two types of organic fiber addition would significantly reduce the risk of this burst behavior. Mix-ing organic fiber can reduce the water evaporation and the mass loss of concrete after high temperature. After high temper-ature treatment, splitting tensile strength of the specimens decreased quicker than the compressive strength. The decrease of strength was obviously enlarged with the increasing of heat holding time. The strength loss after heating would eased by organic fiber, for the in-situ pore structure formed after fiber melted would release a part of stress caused by heating, and prevent the microstructure destruction and explosion of concrete.%研究了不同种类纤维、不同温度和不同保温时间下，混凝土试件高温作用后的质量损失率、相对动弹性模量，进行了抗压强度和劈裂抗拉强度试验，测试其残余强度，讨论了温度、保温时间和纤维种类对其高温后基本物理力学性能的影响，并分析了有机纤维改善混凝土高温后性能的机理。研究表明，高温作用后，基准混凝土性能下降较快，且温度达到700~800℃时，发生爆裂；掺入两种有机纤维都能有效降低混凝土高温作用下的爆裂。掺入有机纤维可以减少高温作用下混凝土的水分蒸发量，降低混凝土的质量损失。高温作用下，混凝土试件的劈裂抗拉强度比抗压强度下降更快。随着保温时间的延长，混凝土的强度损失明显增大。不同纤维均可以降低混凝土高温作用下的强度损失，缓解高温作用下混凝土内应力可能引起的破坏，降低爆裂的可能性。
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