The invention discloses a blue light CdSe nanosheet crystal form regulation and control method. According to the blue light CdSe nanosheet crystal form regulation and control method, reaction temperature is reduced, and reaction time is prolonged based on conventional blue light CdSe nanosheet synthesis, wherein the CdSe nanosheet is prepared through adding of cadmium acetate dihydrate, selenium powder, and oleic acid into octadecene (ODE), and degrassing at inert atmosphere. The advantages are that: accurate regulation and control of reaction temperature and reaction time are adopted, so thatstructure mutual conversion of synthesized nanosheet between face centered cubic zinc blende structure and hexagonal wurtzite structure is realized, and nanosheet crystal structures, emission peaks,and sizes can be adjusted and controlled preferably; and in addition, Se-ODE is taken as the selenium source in conventional wurtzite synthesis technology, in the blue light CdSe nanosheet crystal form regulation and control method, Se powder is taken as a selenium instead of Se-ODE, Se-ODE synthesis time is about 6h, when Se powder is adopted, reaction time is only 3min to 1h, and unreacted Se powder can be precipitated directly, so that centrifugation purification is more convenient.