Ultrafast magnetization precession in the FePt film with weak magnetocrystalline anisotropy is studied using the all-optical method. The magnetization precession is induced by femtosecond laser pulses, and its dynamics is measured by time-resolved magneto-optical Kerr spectroscopy. After fitting and theoretical analyzing, field-dependent and excitation-energy-dependent precession frequency and Gilbert damping factor are obtained. Frequency equation deduced based on micromagnetics and the experimental condition can well explain the nonlinear field-dependence of precession frequency. Frequency is found to increase with the increasing excited energy, and can be attributed to the higher equilibrium temperature. In addition, intrinsic damping factor which is much smaller than that observed in L10-FePt film reported in recent literature is obtained. The effective damping rapidly decreases with the increasing field, and that can be attributed to the magnetic inhomogeneity. Moreover, it is found that increase of excited energy can slow down energy dissipation of the uniform magnetization precession.