The accurate and sensitive quantification of DNA methylation is significant for the early diagnosis of cancer. In this work, an alkaline phosphatase (ALP) triggered in situ fluorogenic reaction between ascorbic acid (AA) and 2,3-DAN was employed as a ratiometric fluorescent probe for the accurate and sensitive detection of DNA methylation with the assistance of ALP encapsulated liposomes. The quinoxaline derivative with a yellow fluorescence emission (I525) was generated from the reaction between AA and 2,3-DAN. Meanwhile, the consumption of 2,3-DAN declined its fluorescence intensity (I386). A ratiometric fluorescent probe (I525/I386) constructed by the above in situ fluorogenic reaction was applied for the accurate detection of DNA methylation. The methylated DNA was first captured by its complementary DNA in 96-well plates. Then, 5mC antibody (Ab) linked liposomes that were encapsulated with ALP recognized and combined with the methylation sites of the target DNA. After the liposomes were lysed by Triton X-100, the released ALP triggered the hydrolysis of ascorbic acid diphosphate (AAP) to form AA, participating in the fluorogenic reaction with 2,3-DAN to produce a quinoxaline derivative. Thus, the ratiometric fluorescence detection of DNA methylation was achieved using I525/I386 values. Using the ALP-enzyme catalyzed reaction and liposomes as signal amplifiers, a low detection limit of 82 fM was obtained for DNA methylation detection. Moreover, the accuracy of the assay could be improved using ratiometric fluorescent probes. We hope that the proposed assay will pave a new way for the accurate determination of low-abundance biomarkers.