<p>Polycrystalline samples of La_0.7Ca_{0.3−<i>x</i>}Sr_<i>x</i>MnO₃ (<i>x</i> = 0.00, 0.10, 0.25) were synthesized via high-pressure heat treatment, and their magnetic properties, magnetocaloric effect (MCE), and critical behavior near the ferromagnetic–paramagnetic phase transition were systematically investigated. X-ray diffraction analysis confirmed that all samples crystallized in a single-phase orthorhombic structure with <i>Pnma</i> symmetry. With increasing Sr doping, the Curie temperature (<i>T</i>_C) shifted from 229 K (<i>x</i> = 0.00) to 336 K(<i>x</i> = 0.25), gradually approaching room temperature. Under an applied magnetic field of 7&#xa0;T, the maximum magnetic entropy change (|−∆<i>S</i>_M|) decreased from 6.06 J&#xa0;kg⁻¹·K⁻¹ (<i>x</i> = 0.00) to 4.92 J&#xa0;kg⁻¹&#xa0;K⁻¹ (<i>x</i> = 0.10) and 4.59&#xa0;J&#xa0;kg⁻¹&#xa0;K⁻¹ (<i>x</i> = 0.25). Despite this reduction, the full-width at half-maximum (Δ<i>T</i>_FWHM) of the entropy change broadened from 70 K to 82 K, leading to a significantly enhanced refrigerant temperature span. Compared with samples prepared by conventional solid-state reaction, Δ<i>T</i>_FWHM increased by 89.19% (<i>x</i> = 0.00), 65.31% (<i>x</i> = 0.10), and 36.37% (<i>x</i> = 0.25). Additionally, the relative cooling power (RCP) improved by 40.71% (<i>x</i> = 0.00), 41.23% (<i>x</i> = 0.10) and 41.62% (<i>x</i> = 0.25). Importantly, pressure application altered the phase transition in the <i>x</i> = 0.10 sample from first-order to second-order. Critical behavior analysis using the modified Arrott plot and Kouvel–Fisher methods revealed an increase in the critical exponent <i>β</i> from 0.460 (<i>x</i> = 0.10) to 0.500 (<i>x</i> = 0.25), indicating that Sr substitution promotes the development of long-range ferromagnetic ordering.</p>