Current differential protection has become a research hotspot in wide-area relay protection because of its fast action and high sensitivity. However, the implementation of wide-area current differential protection has caused a sudden increase in the longitudinal communication traffic between devices. This seriously affects protection performance. This paper proposes a current differential protection principle based on shaping transformation and capacity reduction. This principle transforms the current modulus and current phase of the multi-byte floating point based on single-byte shaping, and the exchange of transformed information can greatly reduce the amount of communication. The differential and braking current are directly calculated without decoding, and a new differential protection criterion is constructed. In addition, the principle of shaping transformation is proposed, the sensitivity of the improved differential protection is analyzed, and the derating rate after transformation is calculated. The protection criterion is verified by PSCAD digital simulation and a dynamic simulation experiment. The results show that this principle can reliably identify the faults inside and outside the area, and has high sensitivity. This work is supported by the National Natural Science Foundation of China (No. 52077120).