Under large-angle conditions, the problem of amplification or even mutation of attitude error would arise in the attitude measurement methods based on accelerometers or gyroscopes. For the large pitch angle measurement, the arrangement of redundant accelerometers can be determined by preset Euler rotation method, which reduces the pitch angle measurement error. For the roll angle measurement under the condition of large pitch angle, a decoupling attitude determination algorithm based on angular rate threshold is proposed. When the actual pitch rate is greater than the threshold value, the angular velocity projection method can suppress the drift of the roll angle error. When the actual pitch rate is less than the threshold value, the angular velocity integration method can avoid the enlargement of the attitude error caused by angular velocity projection. Through theoretical derivation, analysis and simulation, the preset Euler rotation method can effectively avoid the amplification of the pitch angle attitude error under the condition of large pitch angle, and the gyro decoupling attitude measurement algorithm can maintain the roll angle accuracy for a long time in an oscillating environment.