The invention discloses a system for directly measuring the total helium mass flow rate of a primary loop of a high-temperature gas cooled reactor and belongs to the technical field of air mass flow rate measurement. The system comprises an elbow meter set, and a data acquisition and processing device. Single elbow meter comprises an elbow flow sensor, a differential pressure transmitter, a pressure transmitter and a temperature transmitter; the pressure transmitter is used for measuring helium differential pressure inside and outside the elbow flow sensor; the pressure transmitter is used for measuring helium pressure; the temperature transmitter is used for measuring helium temperature; and the data acquisition and processing device is connected with the output ends of the differential pressure transmitter, and the pressure transmitter and the temperature transmitter of each elbow flow meter respectively and is used for calculating the helium mass flow rate according to differentialpressure signals, pressure signals and temperature signals and calculating the total helium mass flow rate of the primary loop of the high-temperature gas cooled reactor by multiplying the helium mass flow rate by a correction factor. The system has a simple structure, is high in reliability and reproductibility accuracy, and does not have additional pressure loss.