According to the computer simulation results for diffusion-limited aggregation in two-dimensional Euclidean space, we give a discussion about some formula for the screening behavior introduced by Muthukumar, Tokuyama, Hentschel and Mutsushita separately. We show that these formula give a large disaggreement with our computer simulation results for a finite system. Then, through the analysis of the process of aggregation by random walk particles, we obtain a equation for the screening behavior that agrees with the simulations in this paper. Finally, we find that the formula introduced by Muthukumar is correct if the aggregate is sufficiently large.