Abstract: Height measurement accuracy is analyzed from InSAR basic theory based on the baseline projection both along horizontal direction and the line of sight direction.The effect formulas of slant range,baseline,phase and height etc.on height measurement accuracy are put forward both mutual influence and non-influence respectively,taking simultaneously into account the baseline projection along horizontal direction and the line of sight direction.It is shown from the formulas that the effect of these independent variables on height measurement accuracy is the special circumstances of non-independence.