The invention provides a high-conductivity soft aluminum monofilament with good heat resistance and a preparation method thereof. The soft aluminum monofilament is prepared from industrial pure aluminum with the purity of more than or equal to 99.7%, Al-B intermediate alloy and Al-RE intermediate alloy, and the Al-B intermediate alloy and the Al-RE intermediate alloy are prepared from the following components of, in percentage by mass, less than or equal to 0.02% of B, 0.1%-0.3% of RE, less than or equal to 0.07% of Si, less than or equal to 0.2% of Fe, 0.012% of (V + Ti + Cr + Mn) and the balance Al and inevitable impurities; and Re is one or two of La or Ce. According to the soft aluminum monofilament, the heat resistance of the soft aluminum monofilament is greatly improved on the basisof improving the electric conductivity of the soft aluminum monofilament, so that the soft aluminum monofilament more meets the requirement of power grid construction.