Abstract: The purpose of this paper is to give a new investigation on the doublet elementary solution method of solving the problem of subsonic flow. A strong singular integral equation is produced. The definition and the calculating formula of the effective principle value of strong singular integral are given. From this integral equation, some numerical methods corresponding to the whole continuous distribution of elementary solution can be deduced. This method is applicable to calculating subsonic aerodynamic force.

Key words: Lienard system, local property, global property