Recently, there are many assaulting events in the United States. It make police’s relationship became nervous. Some analysts said that the property of current assaulting events are mostly "ambush", it make the problem has become particularly serious. It have a connection with protest movement, which is “black lives matter”. What is a black lives matter? It is in recent years the movement in the United States that is against police violence treated African Americans. On July, 2013, Florida white police shot and killed African Americans young people. However, according to the jury’s decision, the police was acquitted on all charges, and it sparked protests. As a result, it began the movement “black lives matter”. The movement of the purpose