This paper has deduced the integral formula of the magnetic induction density and the self-inductance coefficient for circular loop in single-turn according to blot-savart law, and then does numerical calculation with the mathematical software MATLAB. There is a large margin for the error when using the existing approximate formulas in current literatures. For Rx-loop, the error is -18.978% at least. For Tx-loop, the error is -35.84 %~55.65% ; the comparison indicates that the deviations between the single-turn circular loop and the equal area of single-turn square loop in inductance values is 5.12% ~ 8.11%.