To investigate the influence of the Hf concentration and the annealing effect in $Co_{1-x}Hf_x$(X=0.16, 0.24 at.%) systems, ferromagnetic resonance experiments have been carried out. Spin wave resonance spectra for all samples consist of several volume modes and one (or two) surface mode. It is suggested that both surfaces of the film have a perpendicular hard axis to the film plane (negative surface anisotropy). The surface anisotropy $K_{s2}$ at substrate-film interface is varied slowly from -0.07 to -0.32 erg/$ extrm{cm}^2$ and the surface anisotropy $K_{s1}$ at film-air interface is varied from 0.18 to -0.47 erg/ $ extrm{cm}^2$ with increasing annealing temperature in the amorphous $Co_{84}Hf_{16}$ thin films. Also, the surface anisotropy $K_{s2}$ is varied slowly from -0.31 to -0.41 erg/$ extrm{cm}^2$ and the surface anisotropy $K_{s1}$is varied from -0.19 to -0.60 erg/$ extrm{cm}^2$ with increasing annealing temperature in the amporphous $Co_{84}Hf_{16}$ thin films. We conjecture that the variation of surface anisotropy $K_{s1}$ is due to the increase of Co concentration resulted from Hf oxidation for low temperature annealing(150~175 $^{circ}C$) and the diffusion of Co atoms near the film surfaces for high temperature annealing (200~225 $^{circ}C$).