Abstract: A computer simulation study has been carried out to disclose the cause of the fluctuation of ultrasonic integrated backscatter (IB) of myocardium within cardiac cycles.Based on previous experiment data,an ultrasonic backscatter simulation model of myocardial tissues was developed,and the impact of various possible factors on IB has been studied.The preliminary results show that the variation of myocardium thickness is directly relative to the variation of IB,and the impact of the variation of myocardium thickness takes place by changing the geometric arrangement and geometric size,especially distribution density of myocardium fibers.Upon such a result,we are able to explain'the variation of the amplitude and trend of IB fluctuation in pathological cases against that in normal cases,along as many other experimental phenomena.The variation of other factors except myocardium distribution density can also have some effect on IB,and Perhaps their impact can not be ignored,as indicated in our research results.