The occupation mechanism and magnetic transition behavior of trace Zn and P alloying in the sub-rapidly solidified LaFe11.6Si1.4 magnetocaloric plates were investigated. The LaFe11.6Si1.4, LaFe11.6Si1.4Zn0.03, and LaFe11.6Si1.4P0.03 plates were fabricated using the centrifugal casting method in the present work. Experimental results showed that both Zn and P elements were distributed in the La5Si3 and LaFeSi phases during sub-rapid solidification. After annealed at 1373 K for 72 h, the LaFe11.6Si1.4 plate underwent a second-order magnetic transition, while both the LaFe11.6Si1.4Zn0.03 and LaFe11.6Si1.4P0.03 plates underwent a first-order transition. In combination with X-ray diffraction results, it was proposed that both Zn and P atoms prefer to enter the 96i site substituting for FeII/Si atoms according to the density-functional reconstruction of crystallographic structure. The Zn addition led to a slight decrease in magnetic entropy change from 7.0 to 5.9 J/(kg⋅K), while the P addition strikingly enhanced this property to 31.4 J/(kg⋅K) under a magnetic field change of 3 T. The effective refrigeration capacity of the annealed LaFe11.6Si1.4P0.03 plate reached 189.9 J/kg.