In this paper we aimed at investigating the flux pinning property of MgB2 films on hastelloy tapes which are buffered on various thicknesses of SiC layers. We have observed that the increase in thickness of the SiC buffer layer is very closely related with the systematic improvement of the field dependence of the critical current densities (J(c)) of MgB 2 tapes while the values of J(c) decreased. According to the analysis of the pinning force density (F-p), there exist two pinning sources both in the pure MgB2 and in the MgB2 film with the thinnest SiC buffer layer. On the while, the pinning source observed in the MgB2 films with thicker SiC buffer layers appears to be different from those previously mentioned. The different pinning behaviors of MgB2 films may suggest that there be an additional pinning center working on the MgB2 films with thick SiC buffer layers. The microstructural analyses of MgB2 films confirmed that intra-granular defects and columnar grain boundaries may be a dominant pinning mechanism in the pure MgB2 and the MgB2 film with 170 nm-thick SiC buffer layer. For the MgB2 films with thicker SiC buffer layers, carbon diffusion into the MgB2 film, which is defined by the Auger electron spectroscopy, may be the origin of the additional pinning mechanism.