本文旨在提供一個用來分析公共政策變化對市場交易量影響之數量化方法，依市 場特性， 選擇 1,300c.c. （含）以下小型轎車及貨車為研究對象，採用由短邊法則及價格 調整方程式所組成之聯立失衡模型，以民國七十年至民國八十年共十一年四十四季之季資料 ，使用二段最小平方法分別估計其季供需模型；並分別以「零件進口關稅稅率」及「日幣對 新臺幣匯率」之變動對小型轎車及貨車銷售量之影響作政策動態模擬，估計結果及政策動態 之模擬結果與實際現象相符，顯示吾人可經由聯立供需模型得悉零件關稅稅率及匯率變動對 小型轎車及貨車季銷售量之影響，茲有助於政府研訂最適公共政策之參考。

　　　　　The primary objective of the study is to estimate demand-supply models for domestic small-sized passenger cars (below and including 1,300c.c.) and light duty trucks (below and including 1,300c.c.) using demand function, short-side rule and price adjustment equations. Data were collected from Highway Supervision Office and auto manufacturers in the time period of 1981 and 1991 (11-year or 44-season). Two-stage least-square method was used to estimate seasonal demand-supply model. Both models show that the market be in disequilibrium. This estimation results are also examined by component import tariff on public policy simulation as well as Japanese Yem versus NT Dollars Exchange rate on dynamic simulation. The model estimation result and policy & dynamic simulation effect are consistent with actual situation which concluded that disequilibrium model is suitable to analyze short-term market variation and domestic small-sized autos supply-demand belongs to disequilibrium market.