In this Letter, erbium (Er3+) and ytterbium (Yb3+) codoped perovskite Cs2Ag0.6Na0.4In0.9Bi0.1Cl6 microcrystal (MC) is synthesized and demonstrated systematically to the most prospective optical temperature sensing materials. A dual-mode thermometry based on fluorescence intensity ratio and fluorescence lifetime provides a self-reference and highly sensitive temperature measurement under dual wavelength excitation at a temperature from 300 to 470 K. Combined with the white-light emission derived from self-trapped excitons (STEs), the characteristic emission peak of Er3+ ions can be observed under 405 nm laser excitation. The fluorescence intensity ratio (FIR) between perovskite and Er3+ is used as temperature-dependent probe signal, of which maximum value for relative and absolute sensitivities reaches to 1.40% K-1 and 8.20 × 10-2 K-1. Moreover, Er3+ luminescence becomes stronger with the feeding Yb3+ increasing under 980 nm laser excitation. The energy transfer of Er3+ and Yb3+ is revealed by power-dependent photoluminescence (PL) spectroscopy, and the involved upconversion mechanism pertains to the two-photon excitation process. The results reveal that the Er3+/Yb3+ codoped lead-free double perovskite MC is a good candidate for a thermometric material for the novel dual-mode design.