In optical free space coherent communication fine tracking system, the advantage of using fiber nutation or fast steering mirror nutation to detect angle error is reducing losses and simplifying system and so on. However, they both need mechanically moving parts. This paper proposes detection method of the angle error of signal beam without mechanical nutation by acousto-optic deflector. Theoretical model of signal angle error detection is built and the possible error source is analyzed. Meanwhile, the verifying setup is built, and the precision is better than 1/10 angle divergence of signal, which can not affect the heterodyne detection.