稅務案件涉及稅捐核課之行政程序和爭端解決之訴訟程序，兩者皆採職權調查主義，當事人對於待證事實之主張及證據聲請不拘束行政機關與法院，其得依其職權就必要且可能之證據為調查。而因稅務案件量大且相關證據皆處於納稅義務人之管領範圍下，致職權調查待證事實困難，故有當事人協力義務之規範，兩者相互影響。若當事人不盡其協力義務將可能使證明度降低，並於審判最終待證事實仍真偽不明時，以客觀舉證責任為判決分配。本文分析現行法規範下行政與訴訟程序中有權機關職權調查、當事人協力義務、證明度調整與舉證責任之分配，並以營利事業所得稅常見之爭議為例，探討現行實務作法是否與理論一致，並於文末提出相關現行作法之修改或法規範之建議，以供參酌。 / Tax administrative lawsuits involve administrative procedures and administrative litigation. Both administrative procedures and administrative litigation follow the inquisitorial investigation. Tax authorities and courts can investigate the facts and circumstance according to their authority and are not restricted by the declaration of the parties. However, due to the fact of a large number of tax administrative lawsuits and tax information often accessible only to taxpayers, tax authorities and courts may encounter great difficulties in the inquisitorial investigation. Therefore, taxpayers are obligated to assist tax authorities to investigate the relevant facts and circumstance. Taxpayers’ obligation to assist tax authorties may have a counter-effect on tax authorities’ obligation to follow the inquisitorial investigation. When the cooperative obligation falls on the party, it may cause essening of the standard of proof. If there still not knows the truth at the end of final judgment, using objective burden of proof to allocate the judgment. This thesis study the relationship between the inquisitorial investigation of the authority, cooperative obligation of the taxpayer, standard of proof adjustments, and the current burden of proof of legal norms. By examining the tax administrative litigation cases concerning the Profit-Seeking Enterprise Income Tax, this thesis analyzes the discrepancy in the practice and the theory, and concludes with relevant suggestions to improve current practice and legal norms.