This paper presents interpretation of results of a series of monitoring tests on O2, CO2, dust, noxious gases, microclimate, noise and illumination, conducted in seven mining faces of a metal mine, with vertical depths of -30 m, -70 m, -110 m, -150 m, -190 m, -230 m and -300 m. Through research on a vertical trend of a particular factor, several findings can be concluded as follows: concentration of CO2 rises up, while O2 decreases with deeper mining depth; concentrations of noxious gases increase with the deeper mining depth; dust amount exceeds seriously the limit, and grows linearly with the mining depth; dry-bulb temperature, effective temperature and relative humidity demonstrate a linear increase with the mining depth; sound pressure level in mining faces seriously exceed the limit value, and may cause a great harm to miners; illumination values in most mining faces are lower, comparing to the standard. Comprehensive evaluation of environmental quality of faces is carried out by introducing a model of grey clustering combined with G1-method, to determine the weight values and classify quality of the working environment. Results reveal that the environmental quality grade (EQG) of mining faces decrease with the increasing depth. In particular, EQG is excellent when above -150 m exploitation level, at which it becomes mediocre, and changes to bad when below -150 m.