Background: Circulating tumor DNA (ctDNA) has been heralded as a promising tool to detect residual disease, relapse, and monitor treatment response by detecting molecular residual disease (MRD) in solid tumors. Numerous previous studies have demonstrated the molecular characteristics of ctDNA, such as the mutational landscape, single-nucleotide variations, copy number variations, and methylation landscape. Based on the methylation characteristics of ctDNA, we developed a novel MRD evaluation system (PcMM-qMSP) with ctDNA methylation markers, and evaluated the association of changes in ctDNA level with clinical outcome. Methods: We used sequencing data from public databases for data mining by clinical Natural Language Processing (NLP) to screen the pan-cancer ctDNA methylation markers (PcMM). A PcMM-based MRD detection method was established by quantitative methylation-specific PCR (qMSP). Moreover, 99 clinical blood samples [lung cancer (41), colorectal cancer (18), gastric cancer (5), pancreatic adenocarcinoma (16), liver cancer (6), cervical cancer (3), ovarian cancer (4), breast cancer (3), and unknown (3)] were collected to evaluate the consistency of ctDNA level between PcMM-qMSP and next-generation sequencing (NGS). Results: We evaluated the precision, including within-batch (intra) and between-batch (inter) reproducibility. PcMM-qMSP showed coefficients of variation (CVs) of the intra- and inter-batch assay of 0.42-0.65% and 0.05-0.27%, the accuracies were 100%. Best-in-class assays demonstrated a limit of detection (LoD) of approximately 30 copies of methylated DNA, with lower LoD at 10 copies. The evaluation results of 99 pan-solid tumor blood samples showed that the consistency of PcMM-qMSP and NGS in ctDNA level assessment was 0.82. The specific data are shown in the Table. Conclusions: PcMM is a pan-tumor specific methylation biomarker. The results demonstrated that PcMM-qMSP and NGS were highly functionally consistent for estimating ctDNA level. PcMM-qMSP detection time is less than 24 hours and costs USD 300 as compared to NGS, which takes seven days and costs USD 900. Hence, PcMM-qMSP is economical, rapid, accurate and highly sensitive for detecting pan-solid tumors.