Abstract: Some physical process and physical quantity related to the CAPE (convective available potential energy) are introduced in this paper; the essence of CAPE is explained in detail; a new formula is proposed to calculate the CAPE. Then we compare our new formula to the current general formula in an acture case as an instance for three kinds of physical processes: 1) the reversible moist adiabatic process; 2) the pseudo-adiabatic process and 3) constant pseudo-equivalent potential temperature process. The results show that in the case by the MICAPS, the CAPE value from our new algorithm, for the pseudoadiabatic process is obviously higher than that in the reversible moist adiabatic process, and the CIN (convective inhibition) is obviously lower. The result from default computational method of MICAPS is close to that for the constant pseudo-equivalent potential temperature process. So our new algorithm has some advantages.