By using the 1 m telescope of Yunnan Observatories and the 0.5 m telescope of Ho Koon Nature Education cum Astronomical Centre, China, we had obtained eight transit light curves for the exoplanetary system WASP-36 and three for the exoplanetary system XO-3 between 2010 and 2021. By means of the Markov Chain Monte Carlo technique, we have jointly analyzed these light curves and the relative Transiting Exoplanet Survey Satellite light curves to refine the physical parameters of both systems. Through combining the new mid-transit times with the published ones and the ones from the Exoplanet Transit Database website, we have derived transit timing variation (TTV) patterns of the two systems. By analyzing the TTV signals, we find that WASP-36’s TTV favors the apsidal precession model while XO-3’s TTV agrees to the orbital decay model. However, detailed physical analyses demonstrate that the two mechanisms are not the origin of the observed TTVs. Considering that the observed TTVs are induced by perturbers in the systems, based on dynamic simulations, we have constrained the mass of hypothetical perturbers by combining the rms values of both TTVs and radial velocity curve residuals. When the hypothetical perturbing planets are near mean-motion resonance with the transiting planets, the systems could potentially harbor Earth-mass perturbing planets capable of reproducing the observed TTV signals.