Abstract: Advanced particle detector in space applications should obtain the spectrum in 3D distribution of energetic particles, which is required in the current researches of magnetospheric physics. The counter array (CA) is an important part to count the energetic particle in channels more than a thousand. The CA uses a dual-port RAM with 8 bit data port to form a 16 bit count array of 2 048 channels by splitting one counting cycle in two. A prototype of the CA was constructed, and tested with a precision pulse generator and a ²⁰⁷Bi radioactive source. The results show that it is small in size, and has low power consumption, high flexibility and good performances.