The main source and sink of CO 2 in the atmosphere are concentrated in the troposphere.It is of great significance to the study of CO_2 flux and global climate change to obtain the accurate tropospheric CO_2 concentration profile.For the characteristics of high resolution,high sensitivity and fast response of tunable diode laser absorption spectroscopy(TDLAS),a compact balloon-borne system based on direct absorption was developed to detect the CO_2 concentration profiles by use of the 2 004.02 nm,R(16),nu_1+nu_3 line without the interfere of H_2O absorption and the CO_2 density of the number of molecules below 10 km in the troposphere was obtained.Due to the balloon-borne environment,a compact design of one single board integrated with laser driver,signal conditioning,spectra acquiring and concentration retrieving was developed.Limited by the working capability and hardware resources of embedded micro-processor,the spectra processing algorithm was optimized to reduce the time-cost.Compared with the traditional TDLAS sensors with WMS technique,this system was designed based on the direct absorption technique by means of an open-path Herriott cell with 20 moptical-path,which avoided the process of standardization and enhanced the environmental adaptation.The universal design of hardware and software platform achieved diverse gas measuring by changing the laser and adjusting some key parameters in algorithm.The concept of compact design helped to reduce the system's power and volume and balanced the response speed and measure precision.The power consumes below 1.5 Win room tempera-ture and the volume of the single board is 120 mm*100 mm*25 mm,and the measurement accuracy is0.6*10~(-6)at 1.5 sresponse time.It has been proved that the system can realize high precision detection of CO_2 profile at 15 mvertical resolution in troposphere and TDLAS is an available method for balloon-borne detection.