To obtain the transverse deformation properties of reactive powder concrete (RPC) after high temperature, the uniaxial compression experiments were conducted on 180 prismatic specimens with the size of 70.7 mm×70.7 mm×228 mm for reactive powder concrete (RPC) after exposure to 20～900 ℃. The curves of transverse deformation coefficient with the stress ratio were measured for RPC with various fiber types and contents. Then the relationships between volumetric strain and heating temperature were received. The results indicate that the Poisson's ratio of RPC under room temperature is 0.201～0.212. For the same heat treatment, the Poisson's ratio reduces gradually with the increasing of fiber content. After exposure to 20～400 ℃ the Poisson's ratio decreases gradually with the temperature increases, but it restores when the temperature is higher than 400 ℃. The equation to express the relationship between Poisson's ratio and exposure temperature is proposed, and the fitting curve is in good agreement with the test results.