The invention discloses a method for treating byproducts of hydrazine hydrate prepared by the aid of urea processes. The method includes a crude hydrazine preparation step, carrying out reaction on urea liquid and sodium hypochlorite in a reaction tower at the crude hydrazine temperature of 100-110 Celsius degrees to generate the hydrazine hydrate and the byproducts including sodium chloride and sodium carbonate; a distillation step, filling an evaporation system with high-temperature crude hydrazine without cooling, heating the high-temperature crude hydrazine and distilling water to obtain distilled crude hydrazine; a precipitation step, adding magnesium chloride into the distilled crude hydrazine and carrying out chemical reaction on the magnesium chloride and the sodium carbonate in the crude hydrazine to generate precipitates; a separation step, separating the precipitates by the aid of a separator to obtain the precipitates and separated liquid; a desalination step, desalinating the separated liquid by the aid of the evaporation system to obtain refined hydrazine hydrate. The method has the advantages that the sodium carbonate which is the byproduct of the hydrazine hydrate prepared by the aid of the urea processes can be effectively recycled by the aid of simple technologies at a low cost, and the purpose of refining the hydrazine hydrate can be achieved.