The invention discloses a method for preparing hydrazine with urine as the raw material. The method includes the following steps that firstly, a sodium hypochlorite-sodium hydroxide solution is prepared, wherein chlorine is introduced in a sodium hydroxide solution, the sodium hypochlorite-sodium hydroxide solution is prepared, and the molar ratio of sodium hypochlorite to sodium hydroxide in the sodium hypochlorite-sodium hydroxide solution is 1:2; secondly, low-temperature reaction is conducted, wherein the sodium hypochlorite-sodium hydroxide solution is added into fresh urine, so that the molar ratio of urea to sodium hypochlorite to sodium hydroxide in a reaction system is 1.05:1:2; stirring is continuously conducted, reaction temperature is not higher than 15 DEG C, and reaction time is not shorter than 30 min; thirdly, high-temperature reaction is conducted, wherein materials are conveyed into a reaction kettle to be quickly heated to be boiled after reaction, reflux is conducted for 5 min, then discharging is conducted, and hydrazine is prepared. The method can reduce nitrogen loads in urine waste water, denitrification of urine wastewater is achieved, hydrazine high in application value can also be manufactured, and cost of urea raw materials required in hydrazine preparation in chemical plants is reduced.