To study the Built-in determined Sub-key Correlation Power Analysis (BS-CPA) proposed by Yuichi Komano et al.(KOMANO Y, SHIMIZU H, KAWAMURA S. BS-CPA: built-in determined sub-key correlation power analysis. IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, 2010,E93-A(9):1632-1638.) based on the data set of dpacontest.org, this paper compared the efficiency of Differential Power Analysis (DPA), Correlation Power Analysis (CPA) and BS-CPA from the number of power consumption trace and success rate, the result shows that although BS-CPA works out nicely in theory, it is far from the reaching of the efficiency claimed by the authors, and then the intermediate was chosen by the relationship between the statement of executed cryptographic device’s register and power consumption. Attack surface was narrowed by the reduction of noise and ghost peak, the most relative point was filtered out. Compared with the whole point attack, the biggest success rate of partial point attack can be increased by 60% to crack the 64 bit keys for the same number traces. The experiment results prove that the improved model is able to increase the efficiency and decrease the needed power consumption trace for the same success rate, and the result is stable.