A beam dwell time allocation algorithm based on Riemannian manifolds is proposed for the spatial search process of digital array radar. In order to compensate for the gain loss resulting from beam broadening as it scans angles of the broadside， the spatial distribution of beam dwell time in uv-plane is given according to Riemannian manifolds. The dwell time is allocated optimally over the whole space and the transmitting power of beam is minimized under the condition that the one detection probability and the cumulative detection probability of the specified range are satisfied. The simulation results show that the beam dwell time allocation algorithm based on Riemannian manifolds eliminates the effect of beam gain variation caused by the change of direction， and realizes the equal power detection in different directions.