The present invention relates to the field of pharmaceuticals, especially to the field of veterinary drugs, and more particularly to a crystal form of milbemycin A3 oxime, able to be characterized by the X-ray powder diffraction spectrogram, infrared absorption (IR) spectrogram, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA), etc. Furthermore, the present invention also relates to a method for preparing the crystal form of milbemycin A3 oxime and to a use of the crystal form of milbemycin A3 oxime as an insecticidal and acaricidal agent.