Abstract: The majority of the researches about the coverage problem of wireless multi-media sensor networks(WMSNs) are based on 2D sensing model. For video nodes， 2D sensing model cannot describe their sensing range precisely， and the space above the monitoring horizon is generally omitted. Thus， the concept of space coverage was proposed， and a new 3D sensing model was defined. By separating the two factors pitch angles and deflection angles which can seriously influence the space coverage， the Particle Swarm Optimization (PSO) was employed for optimizing the 1-space coverage. By considering the requirements of practical applications， the concept of efficient space coverage was proposed here， which can guarantee the efficient video collection of monitoring targets. At last， the degree of space coverage is significantly improved by means of simulation， which proves the proposed optimization efficient.

Key words: wireless multi-media sensor networks(WMSNs), space coverage, 3D sensing model, PSO