We use two pairs of FBGs to perform simultaneous strain and temperature field measurements. The first pair of FBGs, comprising one uniform FBG and one chirped FBG, measures the strain and temperature fields, while the second pair of FBGs, also comprising one uniform FBG and one chirped FBG, measures the temperature field only. A genetic algorithm is applied to reconstruct the arbitrary strain and temperature distribution profiles simultaneously from the measured reflection intensity spectra of the four FBGs. Also, we include the reflection power attenuation factors into the genetic algorithm and make this approach more useful in practical. Several strain distributions along the fiber Bragg gratings are reconstructed numerically. The proposed measurement method is suitable for many smart structure-monitoring applications.