A new data transmission system used for the ENVI MAG magnetometer has been developed.The system adopts VC++ computer language and can be run under the condition of Windows, like Win95/98/Me/2000/XP.It can be used to dump every kind of data measured with ENVI MAG magnetometer and stored in its memory. It wins advantages over the prior Bindump.exe software offered by the manufacturer which must be run under the DOS condition. The system the authors developed has the merits of rapidness, accuracy and easy operation. It can also directly dump the data coded decimal without transforming from binary to decimal with the Xfenvi.exe software offered by the manufacturer.