The invention specifically relates to a sample preparation method and detection method for water-soluble heavy metal elements in solid waste, belonging to the technical field of analytical chemistry. The method comprises the following steps: a, adding pure water into to-be-detected solid waste; b, adding a neutral oxidizing atmosphere protective agent and carrying out vibrating extraction for 4 to 6 h; c, carrying out filtering, taking filtrate and adding an oxidizing strong acid solution and the neutral oxidizing atmosphere protective agent into the filtrate so as to obtain a mixed solution; and d, maintaining the mixed solution in a sub-boiling state and then successively carrying out evaporative concentration, cooling to room temperature, dilution and volume fixation. The methods provided by the invention have the characteristics of easy operation, a few steps, low requirements on the performance of analysis equipment and experimental condition, small usage amounts of reagents, capacity of simultaneous determination of multiple elements, low quantitative determination lower limit, high precision, etc. and totally meet technical needs for accurate determination of water-soluble heavy metal elements like Hg, Cd, Pb, As, Se, Be, Cr, Cu, Zn and Ni in antimony titanium chloride tailings in an analysis laboratory with common equipment and conditions.