The present invention discloses a three-dimensional parallel electrical prospecting observation system and a geological body exploration method. According to the construction of the three-dimensional parallel electrical prospecting observation system, electrodes are arranged on the ground and in a plurality of holes simultaneously. According to in-hole electrode arrangement, an electrode string is arranged in each borehole, and each electrode string is composed of a plurality of electrodes with fixed spacing, and the length of each electrode string is L. According to ground electrode group arrangement, a grid-like electrode group is arranged on the ground, the spacing of the electrodes in the grid-like electrode group is a, and the grid range of the grid-like electrode group covers the range of a plane of the boreholes where the in-hole electrodes are located. A common electrode B is placed at infinity, and a common comparison electrode N is placed at any position; the common electrode B, the common comparison electrode N, the electrode strings in the boreholes, the ground electrode group are connected through a parallel electric prospecting instrument; and hidden geological anomalies can be identified through multi-hole and ground synchronous electrical prospecting observation.