Nano-aluminum, which has high thermal conductivity and good compatibility, was added into paraffin to improve its thermal conductivity. Surface modified technology was adopted and dispersant was used to prepare uniform and stable organic phase-change nano-fluid of paraffin and nano-aluminum. Transient plane source method was used to test the thermal conductivity of the prepared organic phase-change nano-fluid. Results showed that the addition of nano-aluminum largely improved the thermal conductivity of paraffin. After the formula of Lu and Lin was modified, a calculation model for thermal conductivity of the organic phase-change nano-fluid was deduced. And experimental results showed that the results of calculation agreed that of experiment very well.