The solution is to adjust the Settings_Service.ini files located by default on C:Program FilesMicrosoft Office Web AppsOpenFromUrlWeb and C:Program FilesMicrosoft Office Web AppsOpenFromUrlHost.
C:Program FilesMicrosoft Office Web AppsOpenFromUrlWeb and C:Program FilesMicrosoft Office Web AppsOpenFromUrlHost are the paths behind oh (OpenFromUrlHost) and op (OpenFromUrlWeb) web applications.
Add the following new line at the end of the file, or update it in case already exists. This new setting will configure the Office Web Apps server to render files larger up to 500 MB.
OpenFromUrlMaxFileSizeInKBytes=(System.Int32)512000
Attention: In case you will reconfigure the server to accept such large office files, make sure the network connectivity between the Office Web Apps server and the file share server is good enough. The in-browser loading time of the office document will directly depend on how fast the file is download by OWA server from the source.
C:Program FilesMicrosoft Office Web AppsOpenFromUrlWebSettings_Service.ini
C:Program FilesMicrosoft Office Web AppsOpenFromUrlHostSettings_Service.ini
Restart/Recycle Web App Pool
转自：
http://www.vioreliftode.com/index.php/office-web-apps-2013-file-too-large/