Under the short wave extremely low signal-to-noise ratio condition data transmission militarily is the lowest safeguard correspondence one method.It has the antijamming and anti-multi-diameter ability,the frequency spectrum use factor is high,signal hiding and so on a series of merits.The present paper uses the direct sequence spread spectrum technology,key to short-wave communication and direct sequence spread spectrum correspondence characteristic as well as union advantage,wide frequency code production,the direct sequence spread spectrum communications system technology and the principle,the wide frequency synchronization technology,the RAKE receive technology has conducted the research and the analysis.The knowledge studies which according to oneself and unifies own ability,designed under one kind of extremely low signal-to-noise ratio condition short wave DS-SS communications system.And has carried on the preliminary modular design and the simulation with mathematics software to the system,has laid the rationale for the reality system design.