Abstract:      In the GNSS receiver, it is very common to extract the navigation message caused by bit synchronization errors, such as the failure of the navigation message and the error of the pseudo range. The current bit synchronization algorithm is mainly based on the histogram method. Among them, the histogram method based on hard decision is widely used, mainly because of its convenient implementation, but its low noise ratio is too low, can not meet the needs of the project. Therefore, it is necessary to study the bit synchronization algorithm under low SNR, this scheme adopts the bit synchronization algorithm with the combination of histogram method and software. First, the GNSS signal data is generated at different carrier to noise ratio, and it has 20 bit boundaries. Then, two algorithms are used to carry out bit synchronization. Repeated simulation times, each time the simulation using random bit boundary, get the correct bit synchronization probability of each algorithm in different carrier to noise ratio. The simulation results show that the longer the bit synchronization time is, the greater the probability of the algorithm is. In the low carrier to noise ratio, the soft correlation method is much higher than the traditional histogram method. Then the soft correlation method was implement in altera arriav.