Abstract: The effect of Tm doping on the magnetic phase transition and magnetocaloric effect (MCE) of ErCr₂Si₂-based compounds were systematically investigated. A series of polycrystalline Er_1-xTm_xCr₂Si₂ (0 ≤ x ≤ 0.4) samples were successfully synthesized by the arc-melting method. X-ray powder diffraction combined with Rietveld refinement indicated that all samples crystallized in the ThCr₂Si₂-type tetragonal structure with space group I4/mmm. It was found that with increasing Tm concentration, the saturation magnetization (M_S) decreased from 7.7 μ_B(x = 0) to 6.8 μ_B(x = 0.4). Under a low magnetic field (Δμ₀H ) change of 0-1 T, the x = 0.1 sample exhibited the optimal magnetocaloric performance, with maximum magnetic entropy change (-ΔS_M^max ) of 19.7 J/(kg·K), representing an enhancement of 18.7% compared with the reported undoped ErCr₂Si₂ (-ΔS_M^max =16.6 J/(kg·K)). Moreover, the saturation driving magnetic field H_S corresponding to the magnetic entropy change decreased from 0.45 T to 0.4 T. Tm doping also significantly broadened the effective refrigeration operating temperature window (T_ope). Under a magnetic field change of ∆μ₀H = 0-5 T, T_ope expanded from 14.1 K (2-16.1 K) for x = 0 to 17.3 K (2-19.3 K) for x = 0.4, corresponding to an increase of approximately 22.7%. In addition, both the thermal hysteresis loss (ΔT_hys) and the average magnetic hysteresis loss (W_ave) decreased with increasing Tm concentration, from 0.33 K and 2.28 J/kg at x = 0 to 0.22 K and 0.89 J/kg at x = 0.4, representing reductions of about 33.3% and 60.9%, respectively. Arrott plots, power-law critical exponent fitting, and the universal behavior of the reduced magnetic entropy change curves consistently demonstrated that this system exhibited typical second-order magnetic phase transition characteristics. Its small thermal and magnetic hysteresis losses were considered beneficial for practical applications in industrial magnetic refrigeration.