The 4'*4' Tri-Sonic Wind Tunnel at ASRD/CSIST, starting in 1983, is currently the largest high speed wind tunnel in this country. Its operating range was originally from Mach 0.3 to 4. With the increasing need for tests at higher Mach numbers in the development of high speed weapon systems. By aerodynamics theorem and utilizing the practical operating experience of many years, ASRD successfully found the solution to complete this upgrade program. Other relevant systems adjustment were also executed to support this upgrade program. Testing data from tunnel performance test indicated that the Mach number uncertainty were within the error band, and the maximum flow field uniformity fell from 0.064 to 0.011, proving that a prominent accomplishment was achieved in this upgrade program.