At present, the methods using parallel plates and probes for detecting the plasma in the strong field have some limitations in measuring the charged particles produced by gas with high flow rate at atmospheric pressure. In this paper, a new detector with a spherical probe was proposed and was used to measure the charged particle concentration under the conditions of various gas velocities, electric field intensities and distances, as well as to study the spatial distribution of plasma. The result of the new method when was compared with that of DLY air ion detector indicates that the concentration detected by the former is near to the real value. Moreover, the detector with a spherical probe has advantages of as simple operation, small volume and convenience of local test, which contribute to the research of spatial distribution of plasma.