The leakage caused by concrete cracks was a major challenge for civil engineers, and the approach of microbiological calcium carbonate precipitation provided a new method for solving this problem. There were two methods to seal concrete cracks：direct injection of bacteria liquid and pre filled perfusion before injection. A comparison experimental study on the two sealing methods was performed. The curves of outflow velocity versus grouting times were researched with a special attention on the influence of crack width. The results show that method of direct injection of bucteric liquid works well for small cracks(i.e. with a crack width below 05mm), whereas pre filled perfusion before injection method is a better choice for the large cracks.