By using multi-bands BCS theory, we have calculated the superconductivityenergy gap and the critical temperature of a thin-film metallic superconductor.The thermodynamic superconducting characteristics such as critical magneticfield, specific heat, as well as the tunneling conductance are investigated forvarying film thickness and temperature. We find the oscillation ofthermodynamic superconducting properties with the film thickness, including thethermodynamic critical field $H_c$, the specific heat of normal,superconducting state, and position of the differential tunneling conductancepeak. The two universal constants the nth sub-band energy gap $\Delta_n$ attemperature $T=0K$ over $k_BT_c$, and the specific heat jump at $T_c$ overnormal state specific heat at $T_c$ are independent of the film thickness.Their values are the same as in the bulk superconductor.
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