The present invention discloses a ZUC sequence cipher algorithm mask protection method of which the round output is an arithmetic mask. The method comprises the steps of (1) selecting the number of round needing the masks, initializing the first N rounds, and obtaining the input with masks R1+m1, R2+m2 by a random number; (2) converting the additive operation into the xor operation by a conversion function g(x,y) after adding the mask protection on the input X1 and X2 of each round in the front N rounds separately; (4) carrying out the 16 displacement operation, and the L1 and L2 linear operation; (5) carrying out the SL' and SR' operations; (6) for the W output of an F function, converting into the additive operation by a conversion function h(x,y) to obtain the correct W output. The mask value of each node in the mask protection method operation designed by the technical scheme of the application is different, and the mask value outputted by each round S box is also different, so that the first-order analysis of the hamming weight and hamming distance can be resisted. In addition, the second-order analysis also can not find any utilizable leakage point.