We propose a kind of trench-assisted graded-index ring-core fiber(TA-GI-RCF)with a low refractive index rod deployed in the center of the core,which supports three LP modes(LP01,LP11 and LP21)transmission.There are two difficulties about designing TA-GI-RCF,one is to depart LP21 mode from LP02 mode because their effective index are too close which makes it difficult to realize only three LP modes transmission; the other one is how to make sure these three LP modes reach the receiver end with low differential mode delay(DMD),so that the computation complexity of multi-input multi-output(MIMO)digital signal process(DSP)can be reduced.