La(Fe,Si)₁₃ hydride is regarded as one of the most promising room-temperature magnetic refrigerants. A typical active magnetic refrigerator machine requires thin plate-shaped refrigerants. In this work, plate-shaped LaFe_11.44Si_1.56 hydrides with different particle sizes were prepared by sintering in a high-pressure H₂ atmosphere of 40MPa. Effect of particle size and sintering duration on the structure and magnetocaloric effect was investigated. Compared to the parent alloy, α-Fe contents of the sintered samples are increased and different particle sizes and sintering duration do not remarkably influence the precipitation of α-Fe. Upon increasing of particle size, Curie temperatures of sintered samples slightly increase and are shifted to above room temperature. Hysteresis of plate-shaped LaFe_11.44Si_1.56 hydrides has been almost eliminated due to the existence of micropores with a large size of distribution and small particle size, which reduces the internal strain during the process of the phase transitions. Compared with the sintered sample with particle size from 110 to 150μm, the hysteresis loss of the sintered sample with particle size smaller than 40μm is decreased by 35%, while the large magnetic-entropy ΔS_m maintains. LaFe_11.44Si_1.56 thin plate-shaped hydride with particle size smaller than 40μm exhibits a large change ΔSm of 8.5J/kg.K(53mJ/cm₃.K) for a field change of 1.5T at 345K.