The invention discloses a uni-travelling carrier photoelectric detector and a manufacturing method thereof. The photoelectric detector comprises a substrate, an epitaxial layer and an electrode, and is characterized in that the epitaxial layer comprises an aggregation layer, a cliff layer, a conducting layer, an absorption layer and a barrier layer which are successively superimposed, the absorption layer adopts gradient doped InGaAs, and the barrier layer adopts AlxIn<1-x>As, wherein 0<x<1. According to the invention, the material AlxIn<1-x>As is adopted to act as the barrier layer and the aggregation layer; and the conducting layer InGaAlAs with gradually changing components is adopted to smooth a band gap between InGaAs and InAlAs, so that lattice matching is realized, the dislocation density at a heterogeneous interface is reduced, aggregation of electrons at the heterogeneous interface is prevented, and the drift velocity of the electrons is accelerated. Meanwhile, the doping concentration of the aggregation layer changes in a gradient manner, so that a space charge effect is effectively weakened on the one hand, the thermal power consumption of the device is reduced, and the saturated output current of the device is improved; and one the other hand, a velocity overshoot effect is effectively weakened, and small voltage-dependent bandwidth and better linear response can be acquired.