By describing a model of binary sequential detector realized on a computer

this paper systematically discusses the questions which are unavoidable in implementing a sequential detector for phased-array radar. The efficiency of sequential detection （two steps） is evaluated with retransmitting probability of beam-pointing. After obtaining the operating characteristics of the sequential detector

the relations among the retransmitting probability of beam-pointing

detectable signal-to-noise ratio and a detection threshold （or a quantization threshold） are quantitatively described

and the guideline for the rational use of radar’s energy is offered. Comparing the detection quality of sequential detection with that of density detection

the extent of improvement made by sequential detection for a radar is given. If the value of detection threshold （or quantization threshold） for the radar is properly selected

the sequential detection can improve the tracking ability by more than 3.4dB for the several detectors described in this paper

with a signal-to-noise ratio loss of 1.6dB only.