Developing a fluorescence sensing platform for point-of-care detection of low abundance biomarkers is highly valuable for early diagnosis of disease. Herein, a biomimetic fluorescence-enhanced platform based on photonic crystals and DNAzyme walker was constructed and further applied to visualize and quantify the miRNA-21 in biological samples. The DNAzyme walker was orthogonally activated by the target miRNA-21, which enabled the unlocking of the DNAzyme walker strand and the subsequently repeated substrate cleavage, thus generating enhanced fluorescence signals. Meanwhile, a biomimetic photonic crystals substrate was employed to physically boost the emitted fluorescence signals again, enabling visual detection by naked eyes and quantitative analysis by smartphone. A limit of detection as low as 84.8 pM was obtained and the single base variation in miRNA-21 could also be discriminated. Furthermore, the potential application of this platform was demonstrated in spiked-urine sample and total RNA extracts, showing good agreement with RT-qPCR results. Therefore, the multiple signal amplification strategy-based fluorescent platform has the advantages of high sensitivity, good specificity, good portability and high-throughput analysis, providing a powerful tool for convenient disease diagnosis and health assessment.