Abstract: The direct path interference is highly correlated with the target signals in the bistatic sonar system,so the common adaptive cancellation algorithm is ineffective.A multiple constrained minimum variance algorithm based on null broaden method is given under the condition of knowing the incident direction of direct path interference.The al-gorithm suppresses the direct path interference by imposing linear constraint,but it is sensitive to the estimation error of interference incident direction.So a method of broadening the null artificially is put forward to improve the algo-rithm.The multiple constrained minimum variance algorithm based on null broaden method is intuitive and rapid.The data processing results of computer simulation and lake experiment show that the improved algorithm can eliminate the direct path interference effectively and keeps valid when the incident direction of direct path interference is incor-rectly estimated.