本研究的研究動機係欲探討公費下降對於審計品質之影響。本研究之貢獻在於先使用公費模型作為理論基礎，推論當各種會計師事務所變動同時審計公費下降時對審計品質之影響。再使用裁決性應計項目、ROA（資產報酬率）控制後之裁決性應計項目以及審計意見配合裁決性應計項目間之關係作為審計品質之代理變數，進行實證分析。增額貢獻有下列四點發現，（一）公費下降由原本之大型事務所續簽之審計品質變差。（二）當公司由大型更換為大型同時公費下降，審計品質會降低。（三）當公司由大型更換為非大型同時公費下降，審計品質仍然較低。（四）會計師事務所更換前一年及當年度與DA呈現負相關，在台灣之環境下結果同國外環境之結果相同。

This research uses audit fee model to interpret the relationship between audit fee down, CPA firm change and audit quality. This study uses discretionary accruals, discretionary accruals with controlling ROA and audit opinion to proxy the audit quality. The results show the audit quality of BIG 4 firm is better than Non-BIG4 CPA firm. In addition, audit quality of BIG4 will get worse when the audit fee decrease. When the company changed audited firm from BIG4 to Non-BIG4, their audit quality remained low. When the company changed audited firm from BIG4 to another BIG4, their audit quality became worse. We also find when the company audited by Non-BIG4 CPA firm has higher discretionary accruals; however, they still can get unqualified opinion. When the company changes their audit firm in this year; their previous and this year discretionary accruals are negative, which are the same as previous literatures. We also find the company changing audit firm; the previous year's discretionary accruals is not related to the audited opinions.