In the synthetic test of breakers

the slope at zero-crossing of short-current is an important parameter. Currently

this parameter is mainly determined by manual method

which results in significant error inevitably. With the development of digital measurement system

a better method is introduced to calculate this parameter by computer

based on mathematics analysis of measured data. Two algorithms are proposed in this paper

based on mathematics analysis. Verified by applying those algorithms both on ideal signal and measured data

the algorithms are feasible

and have satisfied the requirement of data processing for high power test.