I try to use multigrid accelating technique in hypersonic flow. but it don't run well. in single block grid ,it runs well.now only three layers of grid ,it can't run. who can give me some explain for it

Please let me know more about ur problem, like ur co-ordinate system(rectangular or cylindrical) , BC, and ur domain, what type of restriction u have used, all this will play a role, more over which smoother u are using also very imp for multigrid methods.