  We consider the quantum Fisher information and spin squeezing in one-axis
twisting model with a coherent spin state $|\theta_{0},\phi_{0}\rangle$. We
analytically discuss the dependence of the two parameters: spin squeezing
parameter $\xi^2_{K}$ and the average parameter estimation precision $\chi^2$
on the polar angle $\theta_{0}$ and the azimuth angle $\phi_0$. Moreover, we
discuss the effects of the collisional dephasing on the dynamics of the two
parameters. In this case, the analytical solution of $\xi^2_K$ is also
obtained.
