The immersed boundary method is an effective technique for modeling and simulating fluid-structure interactions especially in the area of biomechanics.The effect of the regularized delta function on the accuracy is an important subject in the property study.A method of manufactured solutions is used in the research.The computational code is first verified to be mistake-free by using smooth manufactured solutions.Then,a jump in the manufactured solution for pressure is introduced to study the accuracy of the immersed boundary method.Four kinds of regularized delta functions are used to test the effect on the accuracy analysis.By analyzing the discretization errors,the accuracy of the immersed boundary method is proved to be first-order.The results show that the regularized delta function cannot improve the accuracy,but it can change the discretization errors in the entire computational domain.