The improved emission enhancement in surface plasmon polariton (SPP) coupling with an InGaN/GaN quantum well (QW) by inserting a SiO2 layer of lower refractive index between the deposited Ag and GaN layers is experimentally and numerically demonstrated. The inserted SiO2 layer leads to reduced SPP dissipation rate, increased evanescent field intensity beyond a certain depth in GaN, and decreased SPP density of state. The combination of these factors can result in further emission enhancement of QW through SPP coupling. For light-emitting diode application, the elongated evanescent field coverage can release the constraint of thin p-type GaN for effective SPP coupling. More importantly, the reduced SPP dissipation can result in more effective emission in such an SPP-QW coupling mechanism.