A new detection method of weak signal mixed in strong noise is proposed. The method includes theory scheme, hardware and software. It detects and processes signal by using the instrument magnifying technology and single-chip microcomputer control. By means of virtual instrumentation simulation and display, this design provides effective methods to detect µA-level weak signal in piezoelectric infrared detector. Through the experiment of simulate low frequency weak signal detection, the system fully reveals its practicality and superiority in the field of lower S/N signal detection.