The invention relates to a method for forming a lower part semiconductor pattern of a three-dimensional memory and the three-dimensional memory. The method comprises the following steps that a semiconductor structure is provided, wherein the semiconductor structure is provided with a substrate and a stacking layer located on the substrate, the stacking layer comprises a plurality of first materiallayers and a plurality of second material layers which are stacked alternately; a plurality of channel holes vertically running through the stacking layer and reaching the substrate are formed; impurities in the substrate are removed through the channel holes, and a plurality of gaps laterally protruding from the side walls of the channel holes to the substrate are formed in the removing process;a semiconductor material containing a doping agent is formed at the bottom portions of the channel holes to serve as the lower part semiconductor pattern, and the gaps are filled with the semiconductor material. The method for forming the lower part semiconductor pattern of the three-dimensional memory can improve the evenness of threshold voltages of selection gates of the bottom of the three-dimensional memory.