Abstract: There are a large number of nuclides with unknown mass in heavy neutron-rich region, which urgently need to be measured. We propose to measure the mass of ²⁰⁴Pt and other heavy neutron-rich nuclides by using the isochronous mass spectrometry (IMS) at the research facility HIRFL-CSR. In the IMS experiments, the nuclides of interest are produced by using projectile fragmentation and stored in the storage ring CSRe. The revolution times of the stored ions are measured, from which the nuclear masses are extracted. To obtain high-precision results from the IMS experiments, it is required that several ions are stored in the Experimental Cooling Storage Ring(CSRe) simultaneously to correct for the effect of the magnetic-field instability. However, the production cross sections of the heavy neutron-rich nuclides are very small, so that the number of ions that can be stored in the CSRe is too low to fulfill the requirement. To solve this problem, it is proposed to use a production target with two different thicknesses at different areas. In this way, a sufficiently large number of ions can be produced and stored in the CSRe at the same time without reducing the yield of the target nucleus significantly. The simulations show that it is feasible to measure the masses of heavy neutron-rich nuclides at CSRe. The experimental settings are recommended.