Abstract: In the SAR imaging simulation, discrete point target sets are often used instead of continuous targets for echo modeling. An important problem of this method is that the target echo depends on the sampling method, and different sampling methods for the same target may produce significantly different imaging results. Another disadvantage is that the accuracy of the echo model is related to the sampling interval. The small sampling interval leads to a large amount of calculation. In order to solve the problems, this paper proposes a new continuous target echo modeling method, which avoids the influence of sampling method and sampling interval, and greatly reduces the calculation amount. The method is applied to the bistatic FMCW SAR system, which is helpful to understand the relationship between its observation geometry and echo characteristics.