Abstract: More linear combinations with longer wave-length and smaller noise can be formed with triple frequencies，which will accelerate ambiguity resolution. The TCAR and CIR methods are most representative，based on the no-geometry model but these approaches neglect information between satellites. In this paper，a geometry-based step by step ambiguity resolution method is presented，extra wide-lane ambiguities，two wide-lane ambiguities and narrow-lane ambiguities of two ionospheric-free combinations are fixed sequentially. An experiment with real BeiDou observation data demonstrated that for baselines within 10 km，nearly all the ambiguities can be fixed at a single epoch.