The thermocompressor is capable to utilize thermal energy directly to product pressure wave for pulse tube refrigerator. To research its performance, an experimental system of a thermocompressor with an annular gap regenerator and its corresponding numerical model were established. Then the performance was measured with different heating temperatures, charge pressures and working fluids. The trends of the simulation results are consistent with the experimental ones, whereas the insufficient heat transfer between the gas and annular gap, and clearance volume should be responsible for the quantitative disparity. Therefore, a piston with wire-cut gaps has been designed, fabricated, and tested. With the new piston, the experimental results and the simulation show that the thermocompressor performance has been drastically improved. The analysis also shows that the optimum performance condition is gained when the total thermal penetration depth is approximate to the hydrodynamic radius, which provides a principle for better operation of thermocompressor. Crown Copyright © 2013 Published by Elsevier Ltd and IIR. All rights reserved.