Dialkyl polysulfides are generally poor in thermal stability. Effects of reaction temperature and pressure should be investigated on sulfur types produced from pyrolysis of dialkyl polysulfides, which may exist in petroleum light hydrocarbons. Petroleum ether (90-120 ℃) was selected as solvent for each of dimethyl disulfide, diethyl disulfide, di-tert-butyl disulfide, dimethyl trisulfide and diethyl trisulfide, all of which were employed as models of short-chain dialkyl polysulfides for the pyrolysis study. Thermal cracking tests were conducted in a high-pressure autoclave. Gas chromatrography with sulfur chemiluminescence detection（GC-SCD） was utilized for determination of pyrolysed sulfur types distributions. Results showed that temperature and pressure significantly affect pyrolysis reactions of dialkyl polysulfides. Mercaptans, hydrogen sulfide and dimethyl sulfide were main pyrolysis products. Dialkyl trisulfides were first disproportionated to dialkyl disulfides and dialkyl tetrasulfides, which continued to pyrolyze into smaller molecule sulfides. Polysulfides with same alkyls but more atoms of sulfur, or with the same atoms of sulfur but more carbon atoms in alkyls in a molecule were relatively easy to pyrolyze. Initial pyrolysis temperatures of dimethyl disulfide, dimethyl trisulfide and di-tert-butyl disulfide at 1.0 MPa were 213 ℃, 161 ℃, and 143℃, respectively. Higher temperature could promote the pyrolysis reactions. For dimethyl disulfide, with reaction temperature rising from 210 ℃(under related pressure of 1.2 MPa) to 330℃(under related pressure of 6.5 MPa), pyrolysis rate increased from 0% to more than 95%. Higher pressure could inhibit the pyrolysis reactions. At 290 ℃, with reaction pressure increasing from 3.3 MPa to 4.7 MPa, pyrolysis rate of dimethyl disulfide decreased from 90% to 25%. At 210 ℃, with the rise of pressure from 1.2 MPa to 2.4 MPa, pyrolysis rate of dimethyl trisulfide decreased from 36% to 0%. By adjusting temperature and pressure, pyrolysis product of short-chain dialkyl polysulfides could be controlled to some extent.