The invention relates to a one-step RT-PCR (Reverse Transcription Polymerase Chain Reaction) detection reagent kit for Cucumber green mottle mosaic virus and a detection method thereof. The reagent kit comprises the following various agents for a one-step RT-PRC reaction: an upstream primer of Cucumber green mottle mosaic virus, a downstream primer of Cucumber green mottle mosaic virus, a PCR Buffer, Mgc12, dNTPs, an RNA enzyme inhibitor, a reverse transcriptase, a DNA polymerase, positive control containing Cucumber green mottle mosaic virus and negative control containing no Cucumber green mottle mosaic virus and RNase-free ddH2O. The invention has the advantages of simple preparation method and convenient large-scale industrialized production, and the detection method has the advantages of simple and convenient operation, high sensitivity, strong specificity and good accuracy. The whole detection process is accomplished in a PCR tube and suitable for rapid detection of a batch of samples, thereby simplifying the operation procedure, reducing the detection time, avoiding the cross contamination, and improving the detection efficiency.