Objective To evaluate the diagnosis value of urodynamics in patients with benign prostate hypertrophy(BPH).Methods With urodynamic device,the full set of urodynamic exam was administrated in 427 patients with BPH,and the externalsphincter urethral myogram was monitored simultaneously in pressure-flow studies(PFS).The umdynamic finding such as Qmax 、Pdet-Qmax、Popen、DS(descending slope) and post-voiding residual(PVR)were recorded,as well as the situation of bladder detrusor constraction and bladder compliance and urethral sphincter coordination. The bladder outflow obstruction was diagnosed by A-G nomogram，P-Q plot and DS.The IPSS score and prostate volume were also acquired. Results The diagnostic rate of BOO is 81.5％,among them concomitantly detrusor muscle impair in 117 cases(27.4％), decreased bladder compliance in 162 case (37.9％)，urethral sphincter dyssynergia in 148 cases(34.7％)，and unstable bladder in l64 cases (38.4％). The increase degree of BOO show an increasing tendency with urodynamic findings such as Qmax ,Pdet-Qmax,Popen,DS and IPSS score and prostatic volume respectively，however a decreasing tendency with Qmax and bladder compliance. Conclusions The urodynamic exam plays an important role in diagnosis of BOO.There is a positive relation among degree of BOO with urodynamic finding such as Pdet-Qmax,Popen,DS and IPSS score and prostatic volume,however，negative relation with Qmax and bladder compliance respectively.