Sugarcane, an economically significant crop, is facing huge challenges from sugarcane mosaic disease (SMD), primarily caused by RNA viruses. During a regular field disease survey of sugarcane in China in June 2023, sugarcane (LC05-136) leaves from Nanning, Guangxi provinces, displayed a mild mosaic pattern. This differs from typical symptoms of sugarcane streak mosaic virus (SCSMV), sugarcane mosaic virus (SCMV), or sorghum mosaic virus (SrMV). To identify the causing pathogen, we purified virions from sugarcane leaves using the method described before. Total RNA was extracted from purified suspension using QIAamp MinElute Virus SpinKit following the manufacturer’s protocol (Qiagen). Initially, RNA was reverse transcribed using Superscript III reverse transcriptase (Life Technologies) with the primer primK random. Subsequently, cDNA synthesis of the second strand was performed with Klenow enzyme (NEB) and used a specific primer A to amplify. An RNA-Seq library was constructed with VAHTS®UniversalPlusDNALibrary PrepKit for Illumina (Vazyme). The product was analyzed through high-throughput sequencing (HTS) using a DNBSEQ-T7 platform by Chengdu Xinshiji Biotechnology Co., LTD, yielding 108,896,756 raw reads (length 150 nt, total size >10 Gb) and 373968 viral effective reads were identified by Kraken2. Next, Diamond was employed to align the contigs with the NR virus library and aligned by BLASTn. HTS resulted in the identification of five contigs (ranging from 662 to 6697 nt) of sugarcane mild mosaic virus (SCMMV, genus Ampelovirus (related, unclassified viruses), family Closteroviridae). By rapid amplification of 5′ and 3′ cDNA ends (Vazyme), the full length of SCMMV sequence was confirmed showing by BLASTn with a higher identity (98.69%) to a SCMMV isolate PSR07106 (GenBank accession no.MN116751.1), thus we designated it as SCMMV-GX1 isolate (GenBank accession no. PP920681). Neighbor-joining tree analysis of full-length genomes of SCMMV indicates that SCMMV-GX1 is most closely related to SCMMV-PSR07106 but forms a distinct branch. This suggests SCMMV-GX1 has some variations compared to those from other regions. To ascertain whether SCMMV is widespread in sugarcane plantations, we collected 28 leaf samples (included the sample through HTS) from sugarcane plants in Hainan, Guangxi, and Yunnan provinces. These samples, which exhibited varying levels of mosaic symptoms, were analyzed using RT-PCR with specific primers (SCMMV-TF and SCMMV-TR) targeting the 264-bp conserved P24 gene of SCMMV. Amplicons of expected size were obtained from 11 samples: Hainan (4/6), Guangxi (3/8), and Yunnan (4/14) and confirmed by sequencing. Based on sampling data, the estimated field incidence of SCMMV is approximately 2%. It has been reported that both SCMMV and SCBV can be transmitted by pink sugarcane mealybug (Saccharicoccus sacchari). Thus, we tested our samples for the presence of SCBV by PCR and identified a co-infection rate of 72.73% for both SCMMV and SCBV across all the samples. Furthermore, SCMMV-GX1 sample was SCBV-negative and the mild mosaic symptoms were probably caused only by SCMMV. Notably, SCMMV has been previously identified in Africa, the Caribbean, America, and Southeast Asia, and this study represents the first report of SCMMV in China.