The doubly charmed baryon,like the proton and neutron,is formed by three quarks.However,they are different,as such a baryon consists of two heavy quarks (charm-quark) and one light quark,while the proton and neutron respectively contain three light quarks.Therefore the doubly charmed baryon is expected to have different internal structures and properties.For example,its mass is 3-4 times higher than those of the proton and neutron.Studying the doubly charmed baryons can provide important information to understand the three-body bound system,the hadronic interaction and the quark model.