The present study aims to investigate and analyze the combustion process in a squared single-element combustion chamber using gaseous oxygen/gaseous hydrogen as propellant mixture. Propellants are injected at ambient temperature with a shear coaxial injector. All investigations, in particular flame emission, flame structure and its anchoring, are studied through a non-invasive optical diagnostic method, using an optically accessible combustion chamber operated at 20 and 10 bar pressure level. A digital camera was used to detect the flame anchoring near the oxygen post tip. On the other hand, to characterize the flame front and combustion process at different ROFs, the detection of hydroxyl radicals emission was permormed.