The characteristics of InGaAs/GaAs multi-quantum well (MQW) solar cells under concentrated sunlight were analyzed by self-consistent numerical calculation and were compared with GaAs p-i-n cells that have the same structure except for the QWs. Prior to the calculations, the absorption coefficients of the InGaAs MQW cell were determined by fitting the calculated quantum efficiencies to experimental ones. In the simulation, mainly the influences of concentrated sunlight and temperature were investigated. Results of the simulation showed that the rate of the conversion efficiency and open-circuit voltage (V-oc) of MQW cells increased faster than that of p-i-n cells as the light intensity increased, while the rate of efficiency of the MQW cell decreased a little slower than that of the p-i-n cell with the temperature increase. MQW cells compensate for the disadvantage of lower efficiency and V-oc than p-i-n cells in a concentrated sunlight system.