It is well known that a cloud cavitation is one of the most destructive forms of cavitation. The set of equations for the motion of a spherical bubble cloud is formulated. Behavior of bubble clouds are simulated numerically when the surrounding pressure is decreased from 50 kPa to a 10 kPa and then increased to 50 kPa. To study the collapse of cloud cavitation more strictly, the internal phenomena of bubble and the compressibility of liquid are considered in the governing equations. An inward propagating shock wave is formed during the collapse of bubble cloud and the shock wave is focused in the center region of the cloud. This makes a violent bubble collapse, which causes a high emitted pressure from the bubbles, which is several hundreds times larger than the single bubble collapse. Moreover, relationship between the cloud collapse and cavitation erosion is studied.