The invention discloses a method for synthesizing copper diselenide nano-crystals in a polyhydric alcohol-based solution. The method comprises the following steps of: (1), dissolving weighed 0.25mmol of copper chloride dihydrate into 10ml of triethylene glycol, to obtain a stable positive ion source solution, in addition, adding 40ml of triethylene glycol into a three-necked flask, adding selenium powder, and adding 0.1g of polyvinyl pyrrolidone, to obtain a negative ion source solution, wherein the mol ratio of Cu / Se is 1:2, 1:1.9, 1:1.8 and 1:1.7 respectively; (2), slowly heating the negative ion solution, rapidly injecting the positive ion source solution when the negative ion solution is heated to 210-270 DEG C, and carrying out backflow reaction, so as to synthesize the CuSe2 nano-crystal solution. By adoption of the method, the components of a product can be controlled accurately, the phase is stable, the repeatability is good, the cost is low, the synthesizing temperature is low, and furthermore, the synthesized copper diselenide nano-crystal solution is safe and low in toxicity.