本文针对海上捷联惯导与北斗卫星导航系统松组合导航的场景，研究了北斗定位误差的处理方法，通过分析北斗定位误差的来源，指出北斗定位误差在局部区域、短时间内存在常值偏离，该常值偏离可以通过地面差分站发布的差分数据进行补偿。现阶段，北斗系统的地面差分站主要集中在国境内重点区域，对于没有布设地面差分站的国境外区域尤其是海洋区域，常用方法是将北斗定位误差看作噪声来处理，但是这种方法会牺牲组合导航的精度，本文提出的采用卡尔曼滤波状态扩维方法，将北斗定位的常值偏离纳入滤波器状态进行估计，以提高组合导航精度。由仿真算例可知，该方法可有效提升定位精度。

Taking the SINS/Beidou loose integrated navigation as the object, the processing method of Beidou positioning error at sea is studied. By analyzing the source of Beidou positioning error, it is pointed out that there is a constant deviation of Beidou positioning error in local areas within a short time. This constant deviation can be compensated by the differential data released by the ground differential stations. However, at this stage, the ground differential stations of Beidou system are mainly concentrated in the key areas of China. For overseas areas, especially marine areas, where there is no ground differential station, the common method is to treat the Beidou positioning error as noise, but this method will sacrifice the accuracy of integrated navigation. In this paper, the constant deviation of Beidou positioning is incorporated into the filter state. And the Kalman filter state expansion method is proposed to estimate this constant deviation to improve the integrated navigation accuracy. Finally, the simulation examples show that the method can effectively improve the positioning accuracy.