Aiming at the failure problem of aerospace electronic product at the complex space environment, the electrothermal coupling method has been used to analyze the reliability of the ten channels independently adjustable voltage conversion system in package (SIP) module based on integrated forming package, which has supplied the voltage to the remote sensing camera detector. First, the electromagnetic model and thermal model have been made based on the SIP module; second, the electrothermal coupling simulation of three working conditions at normal environment have been made, and the maximum temperature of the SIP has been calculated; then, the maximum temperature of the SIP has been also calculated at vacuum and 45 °C to analyze the performance of this SIP in the space environment; at last, some test have been made of the SIP product. Compared with the measured results, the electrothermal coupling method has much more accurate than traditional thermal method. At normal environment, the simulated temperature relative error is 2.8%. At vacuum and 45 °C environment, the simulated temperature relative error is 9%. This method ensured the performance and accuracy of the design of the SIP, which has verified the reliability of aerospace SIP module at early stage.