Precise magnetization measurements of a half-metallic ferromagnet Co2TiSn with the Heusler type structure have been carried out under pressure up to 1.27 GPa. At ambient pressure, the spontaneous magnetic moment Msexp and the Curie temperature TCexp are experimentally obtained to be 1.993(3)μB/f.u. and 376.76(7) K, respectively. The Msexp is independent of applying pressure. The TCexp decreases with the increase of pressure and the pressure derivative of the Curie temperature dTCexp/dp is estimated to be -3.15(9) K/GPa. Furthermore, the pressure effect on the electronic and magnetic properties of Co2TiSn has been theoretically investigated on the basis of first-principles density functional calculations by using the projector augmented wave method in order to evaluate the half metallicity of Co2TiSn. Both the experimental and the theoretical results under pressure reveal that Co2TiSn is half metal. The experimental results of pressure-dependent magnetic properties are finally discussed on the basis of the spin fluctuation theory for itinerant electron magnetism.