Surface enhanced Raman scattering (SERS) is a highly sensitive spectral analysis technique for ultra‐low trace molecule detection. Conventionally, noble metals like silver (Ag) and gold (Au) are used to prepare the SERS substrates; however, it usually requires careful experiment design and accurate process control, which defers their wide applications in practice. In this paper, a one‐step and low‐cost approach to prepare silver decorated porous carbon (Ag NPs/PCN) films for SERS application is reported. Experimentally, gelatin‐silver nitrate mixed solution was first spin‐coated on the Si substrates to form the thin films, and then, the substrates were carbonized at the different temperatures to obtain the Ag NPs/PCN films. The SERS performance of the Ag NPs/PCN films was evaluated by using the R6G as Raman reporter. Results reveal that the SERS activity is closely related to the spin‐coating rate and carbonization temperature. And detection limit of 10−8 M with the Raman enhancement factor of 1.64 × 106 (10−4‐M R6G) can be obtained on the most optimal substrate. Moreover, large‐scale mapping measurement further evidences that excellent Raman signal uniformity with the RSD of 6.93% also can be achieved. [ABSTRACT FROM AUTHOR]