This paper investigates the effect of waterproofing agents on the mechanical properties and water resistance of reactive magnesium oxide foam concrete. Two water repellents, calcium stearate, and siloxane, were used to modify RMFC. The compressive strength test was carried out on the modified RMFC; the surface contact angle, mass water absorption, and softening coefficient of RMFC before and after modification were determined to study the water resistance of the modified RMFC; and the pore structure of RMFC after modification with calcium stearate and siloxane was further investigated by scanning electron microscope (SEM) and Image pro plus image processing software. and siloxane modification on the pore structure of RMFC was further investigated by scanning electron microscope (SEM) and Image Pro Plus image processing software. The contact angle and mass water absorption of RMFC increased with the increase of the dosage of calcium stearate and siloxane; the softening coefficient increased with the increase of the dosage of calcium stearate and decreased with the increase of the dosage of siloxane; the pore size of RMFC modified by calcium stearate and siloxane was refined and the distribution of the pore size was relatively more homogeneous compared with the blank specimen. Calcium stearate dosage of 2.5% has the best effect on the improvement of water resistance of RMFC, reducing the water absorption rate of RMFC while ensuring that it retains a certain degree of strength after water absorption.