A novel double-foil configuration is proposed to improve the laser to x-ray conversion efficiency from laser irradiating a solid target. One-dimensional radiation hydrodynamic simulations show that the total x-ray conversion efficiency for the double-foil target is as high as 54.7%, which has a 10% improvement compared with the normal target. The improvement is mainly due to the enhanced soft x-ray emissions. Influences of the target geometry parameters on the x-ray conversion efficiency are investigated. Detailed energy distributions and the individual contributions of the two foils to the thermal and kinetic energy terms are presented. It is found that the main energy terms are mostly determined by the first foil, and the enhancement of radiation is attributed to the lower ion kinetic energy of the double-foil target.