As is known， response time of a MEMS infrared （IR） detector is usually measured using a complicated measurement system consisting of a blackbody radiation source， a chopper and a water-cooling apparatus. For such a system， both blocking and hollow patterns in the chopper have certain areas， which consume a certain part of time when the chopper spins at a certain frequency. In conventional measurements of response time， however， it is difficult to exclude the time consumed by a chopper， as a result， a large error is usually introduced into the system. To address such an issue， a response time measurement system for MEMS IR detectors using a fast-pulse laser as its radiation source is proposed in this work. Such a system is able to avoid extra time parameter being introduced by equipment . For a thermopile IR detector， response time measured based on traditional method is 14.46ms， while based on the newly established system， the response time is only 3.13ms. This indicates that the new method can perfectly avoid a 300% time error introduced by the traditional method.