Abstract: Silver nitrate adsorbed on the surface of graphite-phase carbon nitride (g-C₃N₄) was reduced to nano-silver (Ag) particles with sodium borohydride as the reducing agent. g-C₃N₄@Ag composite catalysts with different Ag loads were in-situ deposited on carbon nitride by adjusting the ratio of silver nitrate to carbon nitride. The prepared materials were characterized with the field emission scanning electron microscopy (FE-SEM), the X-ray powder diffraction (XRD), the N₂ adsorption-desorption isotherm (BET), the X-ray photoelectron spectroscopy (XPS) and so on. The in-situ thermokinetic properties of Rhodamine B degradation over composite catalysts were studied with UV-Vis absorption spectroscopy and photo-microcalorimetry-fluorescence spectroscopy. The results showed that when the mass fraction of Ag nanoparticles was 4%, the reaction rate constant of Rhodamine B degradation was 1.55×10^-2 min^-1, and the catalytic activity of Rhodamine B was 1.9 times higher than that of unmodified g-C₃N₄. Under the conditions of 10, 20 and 32 W/m², the reaction reached the maximum apparent heat absorption at about 120 s, followed by exothermic reaction, and the final apparent exothermic rate was 7.293×10^-8, 1.316×10^-7 and 1.162×10^-7 mJ/s respectively. The results are of great significance and potential applicative value to the study of thermodynamics, kinetics and spectral properties of in-situ photocatalysis.