A new approach to evaluate the particle sizes and positions has been deve loped on the basis of their coherent images.According to the experimental and calculated results about the coherent images of steady particles

the paper described the features of coherent images of particles.It is concluded that the characteristics of the coherent images are different from those in incoherent cases

and the more the image deviates from the focus

the more obvious the differences are.From theoretical analysis

the conclusion has been drawn and proved that the normalized intensity distributions of coherent images of particles are the same when their recording far-field conditions are identical.The new method to determine the particle sizes and positions is just based on this conclusion.