In neutral point ineffectively grounding power system, the single-phase-to-earth fault is most likely to occur. Due to the complicated environment when single-phase-to-earth fault occurs, lots of domestic and foreign experts are focus on the related research of related theories and devices. Although varieties of fault line detection theories are emerge endlessly, the results are unsatisfactory. The main reason is that the front channel signal detection, sampling, conversion is inaccurately. For those reason,Combined with zerosequence admittance method, MCGS (Monitor and Control Generated System) touch screen module, ADAM-4117 data acquisition module, front-end circuit module and power resource module are used to develop a new type of fault line detection device in this paper. By this line detection device,the flaw of previous line detection device can be remedied. And the new device which can improve the degree of accuracy and the efficiency in line detection can make the line detection really play a role. And then the stability and reliability of power system will improve. Before then,the line detection device mainly base on DSP and SCM and utilize the zero-sequence current method. The MCGS software is available for many years. But not develop its advantages in line detection field. This combination is the first time. In addition,zero sequence admittance method has never appeared in the actual line detection device. The accuracy and instantaneity of this device in fault line detection are verified through laboratory and actual transformer substation experiments.