Precise control of Cas12a activity is crucial to address incompatibility in isothermal amplification-CRISPR-Cas12a one-pot nucleic acid detection. We developed a light-triggerable circular RNA system for dynamic LbCas12a regulation. By employing circular CRISPR guide RNA (crRNA) or a split circular universal direct repeat region with a replaceable spacer, we resolved the incompatibility between isothermal amplification and CRISPR detection. This system demonstrated robust performance in detecting trace nucleic acids in clinical samples. Furthermore, DNA modifications on circular crRNA enabled CRISPR-Cas12a regulation via base excision repair (BER) enzymes, offering potential for BER enzyme detection and modulation of LbCas12a cleavage activity by BER enzymes. This programmable strategy holds promise for selective gene editing in cells with elevated BER enzyme expression, such as uracil DNA glycosylase (UDG) in colon cancer cells. The circular RNA-assisted approach represents a resource-efficient method with significant potential for medical diagnostics and future clinical gene therapy applications.