Disclosed is a method for assembling a safety device and mounting the safety device on a syringe member before the syringe member is filled, said method comprising the steps of: providing a sleeve, a spring element and a mounting element； introducing the spring element into the sleeve along a mounting direction； introducing the mounting element into the sleeve along the mounting direction； obtaining the safety device； before the syringe member is filled, mounting the safety device on the syringe member by connecting the mounting element to the syringe member.
