This paper presents a fast co-adding algorithm designed to stack the images coming from different channels of QCT in real-time. The algorithm calculates the transformation coefficients for every single exposure to eliminate the effects of the possible shifts of the lenses. The way of reprojection and co-adding applied here is a linear method similar to Drizzle, and a reasonable simplification is applied to accelerate the computation. All the calculation can be finished in about 100 ms on a 3.4 GHz CPU with 4 cores, which matches the needs for the observation of space debris perfectly, while the limiting magnitude is improved by about 0.8. The co-adding results of our algorithm are very close to SWarp's, even slightly better in terms of SNRs. (C) 2017 COSPAR. Published by Elsevier Ltd. All rights reserved.