The invention discloses a side channel energy attack method aiming at SM4 password linear transformation output. The method includes the following steps: S1 selecting bytes to be attacked twice, wherein the corresponding digits input each time are bytes in (Xi+1 Xi+2 Xi+3), the bytes corresponding to the bytes to be attacked are random digits, and others are fixed digits, adopting the side channel energy attack method to first attack bytes of a round key and the fixed digits in linear transformation, conducting corresponding computing on the bytes and the fixed digits of the round key obtained through the two-time attack to obtain the complete round key rki, wherein i= 0, 1, 2, 3; S2 conducting reversible calculation to obtain an initial key through a key expansion algorithm according to rk0, rk1, rk2 and rk3 of first four rounds of the round keys. By means of the analysis method, side channel energy analysis attack aiming at SM4 linear transformation output is achieved, attack times required by attack of the complete key are reduced, and attack efficiency and success rate are improved.