Flow visualization within rocket combustion chambers remains to be a challenge, especially under high pressure and high heat flux. In the present study, glass tubes chamber was proposed to observe the flame in conditions equivalent to those in past test with occurrence of combustion instability. No cooling gas injection was adopted to reproduce the test conditions. Inner / outer glass tube configuration was adopted to separate thermal load and mechanical (pressure) load. This non-cooling configuration survived for more than 5 seconds under chamber pressure of 7.5 MPa. Design and test procedure are herein described.