The invention provides a composite separator membrane which includes a separator membrane and a conductor material coating which is composited on the surface of the separator membrane. The conductor material coating includes a sulfide conductor material. The conductor material coating on the surface of the separator membrane contains the sulfide conductor material, so that during charging and discharging of a lithium ion battery, the separator membrane can supply a path for transmitting lithium ions, so that damage on the charging and discharging performance of the lithium ion battery is avoided due to existence of the path in the sulfide conductor material even the surface of the separator membrane is coated with the coating and the porosity of the surface of the separator membrane is reduced, and meanwhile, a long cycle life is achieved. The invention also provides a preparation method of the composite separator membrane and an application thereof in the lithium ion batteries.