The invention discloses a portable high-sensitivity CO2 detection system. The portable high-sensitivity CO2 detection system comprises a main control chip, a laser temperature controller and a current controller, wherein the laser temperature controller and the current controller are connected with the main control chip; the main control chip is connected with an SD (Secure Digital) card by an SPI (Serial Peripheral Interface) and is connected with an upper computer by a universal asynchronous transceiving transmitter; the laser temperature controller and the current controller are respectively connected with a DFB (Distributed Feed Back) laser; laser emitted by the DFB laser enters a Herroitt multireflection absorption cell after being collimated by an optical-fiber collimator; a photoelectric detector detects spectral signals in the Herroitt multireflection absorption cell, and is connected with a signal conditioning circuit; the signal conditioning circuit is connected with the main control chip. The portable CO2 high-sensitivity detection system disclosed by the invention has the advantages that the integration level is high, the volume is small, the weight is light, the power consumption is low, and outfield experiment and certain flying experiment are convenient; due to the adoption of an embedded type system, a concentration value can be directly obtained and can be stored without subsequent processing of the upper computer; due to the adoption of the multireflection absorption cell, the detection sensitivity is greatly improved.