The initial velocity( q value ) is one of the commonly index for predicting the coal and gas outburst, because the measuring borehole displays a parabolic shape under the gravity drill and the specific structure of the existing instrument, the resistance increases when the instrument goes into the borehole, the time of instrument into the borehole extended, makes it possible to miss the optimal measurement time of q values. Through improving the new measuring equipment of q values, and tested in the field. The result suggested that the improved instrument greatly reduced the time of the instrument into the borehole, thus measuring the q values more accurate. Further, since the coal wall sealing hole opener front resistance and the amount of coal dust accumulation in the front of sealing were reduced, in the same case of the drilled length, the measurement depth was increased.