For quantitative analysis in the particle field, a standard wire is generally used as the scaler for measuring the particle size. In order to understand the effect of the reconstructed wire with a certain depth of field on the experimental results, detail analysis of the intensity distribution and variation of the reconstructed wire at different positions are performed by theory and experiments. The influences of the normal scaling method on the particle image data are pointed out and a new scaling method, the non-in -time scaling manner, is given. Experiment results show that, the uncertainty of the particles size measurement is about 4% by keeping the precision of particle location. This new method can effectively solve the problem, which affects the precision of the particle size measurement. It can be used in practical measurements.