The invention discloses a distributed electrical 
cross device and a 
system and a method thereof for realizing SNC 
cascade protection, and the device comprises a back plate and at least four veneers integrated with electrical cross units; the veneers are inserted into limited slots on the back plate and provided with circuit side service access units, 
client side service access units and back plate access units. In the invention, circuit side service and 
client side service are mounted on the same 
veneer, multiple service access and flexible dispatch such as circuit side service, 
client side service and the like can be realized in the back plate of limited slots, thus adding the function of 
processing multiple services of the distributed electrical cross 
system at a low cost. In addition, except for protection switching on subnet in fault, the invention also can perform protection switching on the 
veneer in fault. Due to introducing a 
multiplex and de-
multiplex module to process subwave long-grade service, the subwave long-grade service in fault also can be protected by the invention.