We establish a single diode laser sensor system to obtain temperature and water concentration in CH4/air premixed flame. Line-of-sight properties are analyzed, but line-of-sight results are not path average values for temperature measurements. The measurements are performed on a flat burner based on scannedwavelength direct absorption spectroscopy using two adjacent water lines at 7153.75 and 7154.35 cm?1. Real-time results are acquired using a data acquisition card with a Labview data processing program. The standard uncertainties of the temperature and water concentration measurements are 2.3% and 5.1%, respectively.