CA mortar is a key component of slab track. It is used as the material for leveling damping structure layer between the rigid track slab and concrete trackbed of slab track in high speed rail. In order to determine functions of CA mortar with low elastic modulus (EM), the beam/plate theory on elastic foundation was applied to the calculation of slab track’s stress. Under the bonding or no-bonding condition, the influence of CA mortar’s EM on the warping stress and displacement of track slab were calculated. Stress distribution of CA mortar under the common effects of train load and temperature gradient was explored, and the intensity requirement of CA mortar with different EM was put forward. Calculation results show that longitudinal and lateral bending moments of base plate both increase with the increasing of CA mortar’s EM; when the CA mortar’s EM is in the range of 50～10000MPa, there is gap between track slab and the mortar and the deformation of CA mortar (50mm thick) is not enough to compensate the warpage of the track slab; with the increasing of CA mortar’s EM, the tensile and compressive stresses of CA mortar both increase under the common effects of train load and temperature gradient, thus higher requirements on tensile and compressive strength are demanded when CA with high elastic modulus is used.