Abstract: A radon progeny continuous monitor was developed. The pump was used for sampling, and radon progeny was collected by filter membrane. The alpha radiation was detected by semiconductor detector, and the pulse was measured by two channel pulse-height analyzer. The potential energy concentration of radon progeny was calculated through deduction arithmetic, eliminating the effects of ²²⁰Rn by measuring alpha counting of ²¹²Po (8.78 MeV). The monitor can continuously work without replacing filter membrane. The measurement cycles can be selected in four modes: 1, 1.5, 2 and 3 h. Microprocessor MCS51 was used for auto-sampling, measurement and calculation. The measurement range is 0.001 5-100 μJ·m^-3. The uncertainty is less than 10% when the measurement value is larger than 0.1 μJ·m^-3.