Abstract：For the CCD serial star images

while the space target is moving

the background is still moving because of the CCD flat is moving. At the same time

because of dithering of CCD flat and some other reasons

the gray value of target is not invariable

so much as to disappear in the background noise. In other words

the trace may be discontinuous. The paper put forward a target trace acquisition algorithm in serial star images of moving background. The algorithm can detect the discontinuous trace of small space target with high accuracy. Originally

the cross projection method is used in background star and target area acquisition. Then

a group of N brightest stars in every image is used to estimate the moving vector of the whole background. Finally

put forward a target trace acquisition method. The simulation experiment is done with two small targets in 16 frame serial sky images (8-bit gray scale image). Results of trace acquisition show that the algorithm can detect both trace of the two targets with high accuracy. The algorithm provides a good way for target trace acquisition of small targets whose trace may be discontionuous.