This paper proposes and demonstrates a novel scheme to improve the traditional Brillouin optical correlation domain analysis(BOCDA) system by combining Brillouin gain and loss effects. Thanks to the net gain measurement between the Brillouin gain and loss, the signal-to-noise ratio of the novel scheme is two-fold enhanced, but a also the scheme system needs fewer devices. We develop a prototype of the modified BOCDA system for distributed strain/temperature sensing by utilizing DMZM, two-level EDFA, polarization scrambler optimized circuit design and data acquisition technique, which has high spatial resolution of 1.6 cm, and high accuracy of 10 με (or 0.5 ℃).