Abstract: Core position reconstruction is the prerequisite and basis for physical analysis of ground cosmic ray detection experiments. Based on the symmetry of the extensive air shower and the characteristics of the detector, this paper proposes a new core position reconstruction algorithm-ellipse fitting method, which is used to reconstruct the core position of simulated data and compare it with the center of gravity method. For the event of cosmic ray protons in the core with energy greater than 1 TeV, the core position resolution is less than 5 m, which is significantly better than the center of gravity method; for the event with energy greater than 1 TeV within a range of 20 m near the array boundary, the core position resolution is less than 10 m. It has significant advantages over traditional methods. Because this method can reconstruct edge events and some out-of-core events under the premise of ensuring accuracy, the utilization rate of the events is greatly increased. For the 1-10 PeV proton event, the area utilization rate of the detector array is about twice that of the center of gravity method.