This paper puts forward pseudo-response spectrum method for calculating the dynamic response of structure caused by harmonic load on the floor, and proposes to use frequency ratio as a new modal truncation index. Combined with engineering practice, the analysis results of pseudo-response spectrum method were compared with the results of existing dynamic coefficient method and elastic time-history method. The contrast results show that dynamic coefficient method due to lacking of considering dynamic properties enough was not able to meet the real response and could not evaluate the comfort of the vibration. The results of pseudo-response spectrum method with suitable mode combination method have the same law of the maximum enveloping value as elastic time-history method. This proved that pseudo-response spectrum method is reasonable, safe and economical, which can provide the basis for engineering design.