We report a method to enhance the sensitivity of coherent population trapping (CPT) magnetometers using a combination of left-handed and right-handed circularly polarized light phase-delay detection and a differential detection scheme. The approach can achieve a four third-fold enhancement of the CPT dispersion signal slope and a three-fold reduction in noises. The proposed method experimentally exhibits a four third-fold magnetic field resolution enhancement in CPT open-loop measurements, and the differential method could achieve a sensitivity of 1 p T/H z at 10 Hz and a sensitivity of 0.4 p T/H z at 50-100 Hz in the CPT closed-loop measurement, which is a four-fold sensitivity enhancement compared to the single-transmitted CPT magnetometer.