Infrared detectors are the core of infrared imaging systems, while readout integrated circuits are the key components of detectors. In order to grasp the performance of circuits quickly and accurately, a method of circuit modeling using Verilog-A language is proposed, which present a behavioral simulation model for the ROIC. At first, a typical capacitor trans-impedance amplifier(CTIA) ROIC unit is showed, then the two essential parts of it, operational amplifier and switch are modeled on behavioral level. The op amp model concludes these non-ideal factors, such as finite gain-bandwidth product, input and output offset, output resistance and so on. Non-deal factors that affect switches are considered in the switch behavioral model, such as rise and fall time, on-resistance and so on. At last time-domain modeling method for noise is presented, which is compared with the classical frequency domain method for difference. The analysis results shows that in the situation that noise interested bandwidth(NIBW) is more than 5MHz, the difference between the two methods leads to less than 1% if the sample rate of noise is larger 4 times of the NIBW