The preparation technology of grapefruit essential oil nanocapsules was optimized by complex coacervation and orthogonal design. Nano-sized microcapsule were prepared with gelatin A and sodium alginate as wall materials, grapefruit essential oil as core material and CaCl₂ solution as curing agent. The effects were investigated, including core-wall ratio, ultrasonic time, ultrasonic amplitude and the amount of curing agent on the particle size of microcapsules. The particle size distribution, monomer reaction and thermal stability of grapefruit essential oil nanocapsules were characterized by laser particle size analyzer, Fourier transform infrared spectrometer and thermogravimetric analyzer. The results showed that the optimum preparation process was as follows: core-wall ratio was 12, ultrasonic time was 10 min, ultrasonic amplitude was 10%, and the ratio of curing agent to wall material was 13. Under these conditions, the average particle size of microcapsules was （210.08±10.12） nm, the encapsulation rate was （65.02±1.18）%; PDI was 0.295, the dispersion of the system was good; Zeta potential was -18.4 mV, the microcapsules had negative charge, and the system was stable. Fourier transform infrared spectroscopy showed that the microcapsules contained characteristic peaks of grapefruit essential oil. Thermogravimetric analysis showed that the nano-microcapsules had good thermal sustained release.