Abstract: The comprehensive experimental investigations are conducted on the compressive fatigue resistant of polyurethane grout materials, which are widely used in maintenance of infrastructure and subjected to repeated loads. SEM and compression fatigue tests were applied to the specimens with different densities. The variation of strain under the cyclic compressive load is recorded. The test results show that strain development under load cycles can be divided into three stages:the first stage lasts for decades of cycles and elastic strain increases gradually; the strain at second stage is relative stable; while at third stage, specimen would be fatigue failure at higher stress level and behave as cyclic hardening at lower stress level. The stress threshold of fatigue, α,is between 0.7 and 0.8 for the specimen of 0.3 g/cm³, and it is between 0.6 and 0.7 for the specimen of 0.5 g/cm³. When fatigue failure happens, the specimen will be bulging perpendicular of the load. Developing of micro cracks in polymer walls and bulking of polymer struts can be observed in microscope images. Besides, a parameter D based on the variation of elastic modulus under cycle loading is proposed to quantify the fatigue failure, and D is more pronounced than strain index when materials undergo cyclic hardening at the third stage at low level.