In this article, we report the detection of ochratoxin A (OTA) with excellent sensitivity with the two-aspect signal amplification treatments. Combining the unique property of magnetic nanoparticles and the high efficiency of the in vitro amplification of rolling circular amplification (RCA), the competitive sensing protocol for ultrasensitive detection of OTA was achieved in about 80min. The excellent magnetic separation treatment could effectively avoid the interference of background fluorescent noise in the sensing system while the RCA could tremendously increase the hybridization sequence for the quantum dot labeled probes and further increase the sensing response signal. Afterwards, two factors affecting the final detection limit, concentration of RCA components and RCA reaction time, were all systematically optimized for the best sensing performance. The response of the optimized protocol for OTA detection is highly linear over the wider range from 10-3 to 10ppb, which is 3 orders improvement in sensing range, and the limit of detection is calculated to be as low as 0.13ppt, which is 10,000 folds improvement compared with the traditional methods. More importantly, given the selected aptamer, this universal signal amplification protocol could be widely applied to other fields by just change the recognition sequence of the aptamer.