The Circular Electron Positron Collider (CEPC) has been proposed as a Higgs factory. The scintillator-tungsten based ECAL (Sc-ECAL) is a particle flow oriented sampling electromagnetic calorimeter designed for the CEPC. The active layers are plastic scintillator consist of 5×45 mm2 scintillator strips. The scintillator strips arrange in adjacent layers are perpendicular to each other to achieve a 5×5 mm2 effective transverse size. Photons from each scintillator strip are read out by very compact photon sensor, SiPM, attached at the center of the strip. A mini-prototype of the Sc-ECAL with 30 layers has been constructed and studied. In this report, optimization of the prototype and preliminary cosmic-ray results will be discussed.