  Beam radii for cone-dominant pulsars follow a power-law relation with
frequency, $\vartheta = (\nu/\nu_0)^k+\vartheta_0$, which has not yet well
explained in previous works. We study this frequency dependence of beam radius
(FDB) for cone-dominant pulsars by using the curvature radiation mechanism.
Considering various density and energy distributions of particles in the pulsar
open field line region, we numerically simulate the emission intensity
distribution across emission height and rotation phase, and get integrated
profiles at different frequencies and obtain the FDB curves. For the density
model of a conal-like distribution, the simulated profiles always shrink to one
component at high frequencies. In the density model with two separated density
patches, the profiles always have two distinct components, and the power-law
indices $k$ are found to be in the range from -0.1 to -2.5, consistent with
observational results. Energy distributions of streaming particles have
significant influence on the frequency-dependence behavior. Radial energy decay
of particles are necessary to get proper $\vartheta_0$ in models. We conclude
that by using the curvature radiation mechanism, the observed frequency
dependence of beam radius for the cone-dominant pulsars can only be explained
by the emission model of particles in two density patches with a Gaussian
energy distribution and a radial energy loss.
