Abstract: The least square stepwise collocation formula is derived according to the induction method, so the self covariance and mutual covariance of the observation signals can be described in detail.Based on the stepwise collocation, the adaptive fusion method is established whose main content is adjusting the self covariance and mutually covariance of the observation signals. The airborne gravity data, satellite altimetry gravity dada and land gravity data are fused by using the two fusion mode, which are the fusion based on observation signals and fusion based on the results of stepwise collocation. The computation results show that the accuracy and reliability of the fusion based on observation signals is better than the other mode. According to the shipborne gravity data verifying, the final fusion accuracy is better than 3.7mgal .