The invention provides a numerical control (NC) code security filtering system. The NC code security filtering system is characterized in that a transmission numerical control program NC code between a process terminal in a system configuration management network and a DNC (Direct Numerical Control) numerical control system is in an FTP (File Transfer Protocol) communication mode, so that data are filtered by taking an FTP application proxy module as a basic module; the FTP application proxy module is used for receiving the numerical control program NC code in an industrial firewall, and analyzing, filtering and controlling the data; data which are accordant with a rule are allowed to pass, and data which are not accordant with the rule are blocked and recorded in a log. By adopting the numerical control code security filtering system, the security risk of a numerical control machine tool NC code is lowered, and the technical problems that codes are tampered, sensitive information is leaked and the like are solved.