The invention relates to a groundwater detecting device. Wherein the lower one of two adjacent screw nuts is defined as a lower screw nut, and the upper screw nut is defined as an upper screw nut; thelower screw nut has a lower screw nut shifting position upwardly shifting along a corresponding rotation stop key and a lower screw nut rotation position that is disengaged from the upper side of thecorresponding rotation stop key and rotates with a drive screw in the process of driving with the drive screw; The drive screw has an optical axis segment corresponding to the upper screw nut; the upper screw nut has a upper screw nut fixed position cooperating with the rotation stop of the corresponding rotation stop key and corresponding to the optical axis end, a upper screw nut shifting position upwardly shifting along the corresponding rotation stop key driven by the drive screw and a upper screw nut rotation position that is disengaged from the upper side of the corresponding rotation stop key and rotates with the drive screw; The upper end of the lower screw nut is provided with a pushing structure for pushing up the lower end of the upper screw nut to move the upper screw nut fromthe upper screw nut fixed position to the upper screw nut shifting position. According to the groundwater detecting device, a groundwater detecting device is provide in which a sample chamber can hold several liquid samples.