Exploring the thermometric properties of UCNPs is of great importance for non-contact fluoresce thermometers. Ln-dopedji-NaGdF4:Yb3+,Er3+ upconversion nanoparticles (UCNPs) have been fabricated by varying the ratio of citric ions to molecules in precursor. Morphology of the as-prepared beta-NaGdF4:Yb3+,Er3+ UCNPs turns from hexagonal prisms to agglomerations of smaller particles with decreased dimension. Luminescence intensity decreases and red-to-green ratio increases with increasing ratio of citric ions to molecules. A dual-mode thermometric property has been found in the as-prepared beta-NaGdF4:Yb3+,Er3+ UCNPs. The first mode derives from the temperature dependent fluoresce-intensity-ratios of thermally coupled manifolds of EP3+ (H-2(11/2)) and (S-4(3/2)) manifolds, of which the maximum relative sensitivity value is 0.0036 K-1. The other mode derives from temperature dependent red-to-green ratios, which is a linear function of temperature and the maximum relative sensitivity value is 0.0238 K-1. The beta-NaGdF4:Yb3+,Er3+ UCNPs with morphology of agglomerations of smaller particles with high surface-to-volume ratios show advanced sensitivities, which are suitable for noncontact optical thermometer.