An OLED display device and a manufacturing method thereof are provided. The manufacturing method of the OLED display device realizes the effect of a plurality of non-connected OLED light emitting layers by providing an inverse trapezoidal photoresist in an interval region of a plurality sub-pixels. The produced OLED display device does not have lateral current forming an entire surface distributed cathode over the plurality of OLED light emitting layers of the common layer, that avoiding cross color phenomenon caused by carrier migration between adjacent sub-pixels and ensuring better display effect of the OLED display. Also, by fabricating an auxiliary cathode above or below the cathode and connected thereto, the sheet resistance of the cathode and the uneven brightness caused by voltage drop can both be reduced.