Indium phosphide (InP) polycrystals were synthesized using the horizontal gradient-freeze method. The influence of different temperature gradients on the ratio of polycrystals was analyzed, The results show that the crystals are indium-rich with a ratio of less than 97% when the temperature gradient is lower than 4℃/cm, and the crystals are stoichiometric with a ratio of more than 99% when the temperature gradient is above 5℃/cm. The impurities and electrical properties of the polycrystalline samples were analyzed using glow discharge mass spectrometry (GDMS) and Hall tests. The purity of stoichiometric InP polycrystals was greater than 99.99999%; the carrier concentration was less than 8×1015cm-3; the mobility was greater than 3900cm2·V-1·s-1. The impurities in the polycrystals primarily included Si, S, Fe, Cu, Zn, and As. The sources of the impurities and their effects on the properties of the materials were analyzed.