The LHAASO-ENDA (Electron Neutron Detector array) array will consist of 400 special electron-neutron detectors (en-detectors) developed at Institute for Nuclear Research of Russian Academy of Science (INR RAS) for the PRISMA project. The main feature of the array is capability to simultaneously measure both number of EAS electrons and number of secondary neutrons produced by high energy hadrons in surrounding matter. Electron/neutron ratio was found to be a good parameter to separate different primary nuclei and also to search for gammainduced showers. Detailed Monte-Carlo simulations for the first-step array of 64 en-detectors is now performing. Mass composition analysis with machine learning techniques for Monte-Carlo simulated events is presented