To study the evolution of the intrinsic stress in chemical plating processes, a method based on optical grating sensing model was presented for online monitoring the intrinsic stress evolution. By recording the centre wavelength shifts of Fiber Bragg Grating (FBG) and combining with a bare grating used for compensation, this method has realized the online monitoring of the intrinsic stress. The copper chemical plating experiment was used as an example for the online monitoring. Results show that, the centre wavelength of monitoring FBG presents a blue shift during the copper chemical plating processes. The intrinsic stress serves as a compressive stress on the FBG, which increases with the increasing of the plating time. The stress sensitivity and the precision of the monitoring FBG is 4.10 pm/MPa and 0.24 Mpa respectively.