In this paper, the purple sweet potato pigment was firstly extracted by ultrasound-assisted solvent extraction method, and then its pH sensitivity and light stability were discussed. Finally, purple sweet potato pigment was prepared into spraying print ink and printed into indicator labels to investigate its color difference changes in the atmosphere of food deterioration. The experiment found that the color of purple sweet potato pigment solution changed with the change of pH value. When the pH value changed from 4.0 to 11.0, the purple sweet potato pigment solution gradually changed from pink to green. When the pH value continued to increase, the solution presented a light green color. Purple sweet potato pigment was stable in dark or indoor natural light environment, but outdoor light had great influences on its stability. The spraying print ink was made from 50% ethanol aqueous solution with 30 g/L purple sweet potato pigment dissolved in it. The surface tension of the spraying print ink was 30.92 mN/m, the ink viscosity was 2.48 mPa·s (20 ℃) which met the specified range of inkjet ink surface tension. The color differences (ΔE) of the indicator label in the simulated atmosphere of food deterioration basically met the requirements of human eye recognition.