To cope with the positioning problem of navigation receiver in weak signal condition,a strapdown inertial navigation platform was built to assist satellite navigation system.In this platform,we selected the ADXL345 which is the three-axis digital accelerometer produced by Analog Devices,Inc.,its digital output data can be accessible through either SPI or I2C digital interface.The ADXL345 outputed data under the control of the CPLD,and it was used to frame together with the gyro output data in the MCU.The data frame was sent through the RS232 serial port to the navigation computer where the strapdown inertial calculation was completed and the ancillary information was provided for satellite navigation system.As a key component of inertial measurement unit,ADXL345 is stable and easy to use.Its 10Hz output rate and about 3.9mg/LSB scale factor in full-resolution mode meets the need of the platform design.And the experimental results show that the horizontal accuracy of coarse alignment of SINS is 0.15°.