The electromagnetic properties of magnesium silicate cement were measured by waveguide method. The effects of magnesium-silicon ratio and curing temperature were analyzed and then the mechanism was analyzed based on the microscopic test results. The results show that the early age strength of magnesium silicate cement paste could significantly be enhanced by increasing the curing temperature. The real part of the complex permittivity increases with the increase of magnesium-silicon ratio and curing temperature. The imaginary part of the complex permittivity and the tangent of the loss angle increase by improving curing temperature. To compare with magnesium-silicon ratio， the transmittance， reflectivity and absorptivity are more obviously affected by the curing temperature. The microscopic test results indicate that the water content and pore structure have an important influence on the electromagnetic properties of magnesium silicate cement paste.