In internal combustion engines, severe knock is a destructive phenomenon that would converge the energy released by fuel burning to damage the piston so that the engine can't work anymore, which should be avoided. The destruction mechanism have been revealed in previous researches in which the focusing of shock waves is considered as a main reason to cause the energy convergence and the destruction. However, the method to alleviate such shock wave focusing hasn't been put forward yet. Based on the destruction mechanism proposed before, in this research, a concave combustion chamber has been designed to alleviate the energy convergence of shock waves under severe knock so that the destruction of the piston under severe knock can be avoided. To validate the alleviation effect of the concave chamber, detonation bomb experiments have been conducted separately for the typical cone chamber and the redesigned concave chamber. Four pressure sensors installed in different positions of either chamber were used to monitor the shock wave behaviors and compare the energy convergence intensity for both of these two chambers. The experimental results prove that the concave chamber can efficiently alleviate the energy convergence in the center region. Furthermore, a series of numerical simulations have been conducted to reveal the alleviation mechanism of the concave chamber. Two kinds of alleviation mechanism have been obtained which are separately: the shock wave diffraction and the shock wave breaking up. These mechanism can efficiently alleviate the energy convergence of shock waves. The research results can be used as a theoretical basis for the chamber design to avoid the destruction under severe knock.