The photoelectric characteristics of GaAsSb/InAlAs separate absorption， charge， and multiplication （SACM） avalanche photodetectors were investigated. This heterojunction has a small conduction band offset （=0.089 eV）， which facilitates carrier injection into the multiplication region. Three SACM APDs were designed with charge layer doping concentrations of 2×10¹⁷ cm^-3， 3×10¹⁷ cm^-3， and 4×10¹⁷ cm^-3. Results show that the device with 4×10¹⁷ cm^-3 exhibited the best performance. At room temperature， it achieved a cutoff wavelength of 1.7 ， a punch-through voltage of -10.8 V， a gain of 20.3 at -34.6 V， and a corresponding dark current density of 0.058 A/cm2. Compared with the GaAsSb PIN APD， the gain increased by 6.8 times， and the dark current was effectively reduced. Adjusting the charge layer doping concentration suppresses the dark current and improves the gain， providing a new approach for highly sensitive short-wave infrared APDs.