A drect iteration-based injection current type thermoacoustic conductivity image reconstruction method is disclosed and comprises the following steps: in a first step, injection current type thermoacoustic signals of an object body are obtained; in a second step, a time reversal method is used for obtaining a thermoacoustic source of the object body according to the thermoacoustic signals; in a third step, an initial value of conductivity is given, and an electric scalar potential is solved; in a fourth step, new conductivity is solved; in a fifth step, the conductivity is solved via iteration. The method comprises the following specific processes: the time reversal method is used for obtaining thermoacoustic source distribution on a certain fault plane, an interpolation method is used for obtaining an overall thermoacoustic source of the object body, the initial value [sigma]0 is given, the electric scalar potential [phi]1 is solved via the known [sigma]0 based on a current continuity theorem, the electric scalar potential [phi]1 is substituted into a relational expression for the thermoacoustic source and the conductivity, updated conductivity [sigma]1 is obtained, [sigma]0 is replaced with [sigma]1, and the above processes are repeated till relative error of the conductivity satisfies epsilon=||([sigma]i-[sigma]i-1)/[sigma]i-1||2<=epsilon0.