In astronomical observations, the radio frequency interference (RFI) will cause pseudo spectra and reduce the reliability and validity of observational data. The RFI mitigation which includes many technical means of devices and methods of data processing aims at reducing the influence of RFI on radio astronomical observations. Various efforts were made to improve the anti-RFI capability of the multibeam receiver (Superconducting Spectroscopic Array Receiver, SSAR) of Delingha 13.7 m telescope. The interference transmission path was analyzed. The concepts of device RFI direct coupling coefficient and device RFI system coupling coefficient are proposed. The proportions of interference introduced in receiver system by devices were quantified, and the interference-susceptible devices in the system were located. After the anti-RFI treatment of the interference-susceptible devices, the anti-RFI capability of the receiver system is improved by 30 dB in average, and the astronomical observation efficiency of the telescope is increased by more than 10%.