Recently the discovery of superconductivity in the quasi-1D Rb2Cr3As3 with TC=4.8 K has attracted considerable interest. The unconventional superconductivity has been revealed by both experimental and theoretical investigations. As theoretical calculations have pointed out that A2Cr3As3 is near magnetic order and SC is relevant to strong spin fluctuations, we propose to carry out muon spin rotation and relaxation measurements on Rb2Cr3As3 using the MUSR spectrometer to probe the superconducting state, nature of the gap, pairing mechanism and order parameters. We have already carried out the musr measurements of K2Cr3As3 and Cs2Cr3As3 ( D. T. Adroja, ea al. , PRB 92, 134505 (2015) and D. T. Adroja, ea al. , JPSJ 86, 044710 (2017) ),and found that the superconductivity in these system is related to the magnitism . We would like to measure Rb2Cr3As3 for comparison.