The first 33 detectors for the electromagnetic particles at LHAASO project were installed on Feb. 4, 2018, which  formed the ground-based particle detector array with an area of about 1 mu. All the installed detectors passed the test, achieved stable operation and successfully observed cosmic ray events. Led by the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences (CAS), the development of the detectors for the electromagnetic particles was jointly completed by organizations including Tsinghua University, Shandong University, and Hebei Normal University.