There were a large number of studies about the influence of the speckle statistical characteristics on single pixel imaging system, but effect of speckle density on the system was not reported. The scene images of 1 bit and 8 bits were studied by computer simulation, and the results show that the quality of the recovered images will be better with increasing of sample number. In the case of 1 bit image, the quality of the recovered image will be good and then poor with increasing of speckle density, and the best image can be obtained in the middle value of speckle density. However, for 8 bits image, when the sample number of speckle is small, quality of the recovered image will be good and then poor with increasing of speckle density, and vice versa. The more speckles are employed, the better recovered image can be obtained. However, it can reduce efficiency of the single pixel imaging system. The research of speckle density provides a good reference to overcome this shortcoming, and has certain practical application value.