In the article the diagnostic and regulation problems are considered for the rheological characteristics of mortars which are used for pumping into the interpipe gaps or cracks during repairing the pipelines, tunnels, and other objects. It is important to obtain the necessary mortar viscosity which allows providing a complete hole filling. For this aim the experimental dependencies have been determined between the injection mortar viscosity, the water-cement ratio, and the additives quantity in the mortars. According to the Poiseuille’s flow law the theoretical dependencies have been obtained between the penetration depth of the injection mortar and viscosity under the different water-cement ratios. The said dependencies are a base during the development of the functioning algorithm the diagnostic and regulation system of the injection cement mortars rheological characteristics. The description of this functioning system is given. The mentioned system application allows increasing the cementation quality, corrosion resistance and durability of the repaired pipeline sections as well as decreasing of the work duration and labor costs.