To analyze the microscopic imaging characteristics of wear debris for full field-of-view online visual ferrograph (OLVF), a new reflected light microscopic imaging model is proposed. First, by taking the lambert-cosine law and the small-angle scattering theory as references, a reflected light irradiance model based on the wear debris microscopic imaging is formulated. The microscopic imaging sharpness of wear debris is evaluated quantitatively. Then, according to Matlab simulation calculation of contrast transmittance, the optimized value of optical magnification and the numerical ranges of oil attenuation coefficient detected by full field-of-view OLVF are determined. The changing rules of microscopic imaging sharpness of wear debris are investigated and determined successfully by analyzing the effectiveness of the numerical increasing of oil attenuation coefficient on contrast transmittance. Simulation results show that, under 2. 0× optical magnification and less than 2. 0 oil attenuation coefficient, wear debris deposites near the optical axis of object field of view. And the high-quality microscopic imaging of full field-of-view OLVF for detecting wear debris can be achieved. Finally, the experimental measurement of wear debris microscopic imaging is implemented by using the current full field-of-view OLVF. Results show that the full field-of-view reflected ferrograms of wear debris can be reliably obtained from different in-use lube oils with less than 2. 0 oil attenuation coefficient. It has potential for online wear monitoring by extracting the visual feature information of wear debris.