The influence of steel fiber volume fraction, type and content of expansion agent on the size effect of compressive strength and shrinkage characteristic of ultra high performance concrete(UHPC) were studied. The 40mm and 100mm cube compressive strengths of each samples after curing 28d were tested. The shrinkage characteristics of each samples within 180d were also measured and the starting point is 27h after casting. The results show that, if the 40mm cube compressive strength is the control strength, conversion coefficients of 100mm cube compressive strength of UHPC with and without expansion agent are 074080 and 075080, respectively. The autogenous shrinkage of UHPC accounts for 870% to 927% of its free shrinkage, and by adding steel fiber the free shrinkage of UHPC can be reduced effectively. As for EA1, its hydration rate is too fast and a lot of water is consumed during the early hydration stage of UHPC, a severe self desiccation effect will be seen. As a result, UHPC with EA1shows a larger free shrinkage value than UHPC without EA1 As EA2 can react with the water vapor in the air and the water inside the sample and produce a continuous expansion effect, attention should be paid to control its dosage to ensure the volume stability of UHPC in the practical application.