In this paper, microcapsules with narrow-size distribution, in which the core materials are a kind of suspension containing pigment scarlet powders dispersed in dyed tetrachloroethylene with Span-80 as an emulsifier, are prepared by complex coacervation through controlling sodium dodecyl sulphate (SDS) concentration and agitation rate. The microcapsules, formed in optimized process of 0.01 wt% SDS and 800 rpm, are similar to 40 mu m in diameter. The phase diagram for the gelatin/SDS/water system indicates that the concentration of SDS in the experiments is outside of the complex formation zone to form a gelatin-SDS complex. Consequently, SDS preferential adsorbs and enriches on the surface of the core droplets due to its higher surface activity. Then, gelatin deposits with SDS at the core droplet/water interface to form a primary layer of complexation. Subsequently, with the pH lower than the isoelectric point of gelatin, complex coacervate of gelatin and gum arabic grows on the primary layer surface and finally deposits on the droplets to form a secondary layer. On the whole, the research indicates that the existence of SDS not only decreases the droplet diameters and centralizes the droplets size distribution, but also accelerates coacervation of gelatin and gum arabic to reach the core droplet/water interface, forming no aggregating microcapsules.